We cannot verify this tale. Anton Bosschaert asked a question to the government of Bascara in the province of Gerona and received an exhaustively report. Hereby a translation of this report:

"The place Báscara can also be named Boscara. The difference doesn't matter. Its name is Báscara, but historical writers may have adapted the name. That is why the difference doesn't matter.
People assume, that Báscara is the old Deciana that occurs on the cards of Ptolemeus. In the will of Pedro the Castellnou, bishop of Gerona, it is named as Sancti Accicli the Baschera. In a description of an alodium anno 1140 by Ermengardis for the diocees of Gerona, the city is also called Sancti Aciscli the Baschera.
It is difficult to verify if a feudal has travelled from Báscara to the (current) Belgium between the years 1200 and 1550. He even might have accompanied Karel V. (Observation: it is almost impossible that the requested noble man belonged to the consequence of Karel V: you have to search in a much former period.) During that period several counts of Ampurias and bishops of Gerona have paraded through the streets of Báscara. Báscara was reighned by Pedro III the Great and Pedro IV the Holy.
Between 7 and 12 October 1466 Queen Juana Enríquez, the mother of Fernando the Catholic, took back the area under her sovereignty, during the civil war against the throne applicant Renato de Anjou. The bishop Arnaldo de Montrodó and his retinue have left Báscara in 1341, because of a banishment based on the shameful extortions of his subjects and because of his interference in the plans of the king of Mallorca. They were hunted, as a punishment that was applicable for criminals.
A lot of noble men claimed a religious or notorious office, and also soldiers and Catalans lived in the castle.
Pedro and Ramon de Gallinés, father and son from the house of Gallinés, established themselves in 1326 in Báscara. The son was captured for a personal reason in the castle of Sobreporta in the city Gerona. In these years we find the names of the noble men:Zafont, Cella, Tafurer, Crosas, etc. and later: Ferrer, Vila, García the Oñate, the Miguel, etc. While Báscara were a feudality of the diocese of Gerona we know a lot of feudal lords: (Hereafter a table with names from 1196 until 1554. This table does not contain the name Bosschaert nor any possible derivative names).
One cannot discover an agreement in coats-of arms of Bosschaert and Báscara. Two heraldic weapons excisted, but they were chopped away as a sentence for the crime of betrayal against Philips V during the succession-war. These coats-of-arms were of partisans of the archduke."

In the Antwerp city-archive a file of 'Bisschops and de Donnet' contains a French text, from un unknown author. Hereby the found document and the English translation: "Certain authors have wanted to link a tribe father to the family of Bosschaert who was a feodal lord in Boscara, feodality of Gironne and Catalagne. Most genealogists will have confirmed this Spanish origin. This family will have established themself at the beginning of the 15th century in Antwerp. Afterwards several tribes have arisen with branches in Spain, the Netherlands, Flanders, Germany and even Mexico. All this is however based on a fantasy and must be reffered to as a tale. The family Bosschaert is thorough of the Antwerp origin and its nobility dates from the 17th and 18th century. The valid genealogy of this family indicates at the end of the 16th century a tribe father as a 'coopman' (merchant) and his son was a 'vleeshouwer' (butcher). Others try to prove our ancestors were 'chevaliers de Calatrova' (knight of Calatova) and 'hidalgos Espagnol ' (of a Spanish origin)". A critical reader must conclude that this sincere indignation is slightly out of place. One categorical negative letter cannot erase the reality. And that reality is, that we do not know the truth. There is absolutely no starting point.

On a Spanish document Anthony has found a heraldic clue: The coat-or-arms of Báscara or Boscara as tree uprooted trees of gold on a green field. This coat-or-arms appears in the 11th century and is carried in the 14th century in Tarragona by Ramon Berenguer, San Olegario and also in the beginning of the 12th century by the Norwegian knight Robert Bordet. The Bascara's fought with the Catalan fightertroups in Lepanto at the command of Don Juan of Austria. In Antwerp we have found similar coat-of-arms: always three (arid or uprooted) trees, surrounded with 3 lapwings of blackbirds. The number '3' might also mean something.

The author E. de Steins of "Universel, Panthéon Biographique" (1850) assumpts that Guillaume Bouschaert, originating of Boscara (in Spain, not far from Gerona in Catalonia), was married with Giacomelle de Neufville. His (grand)grandchild established as an alderman in Antwerp. Link to this genealogy
And thus starts E. de Steins the Bosschaert genealogy. This seems a rather improbable theory, but yet it cannot be refuted.
In "Nobiliaire the Belgique" by Van der Heijden this theory is reused and ‘corrected’; also without any source indication. The (grand)grandchild Jacobus was then married with Lysbeth van Haubraecken.
The analogy between Boscara, Bouschart and Bosschaert is easy: original pronounced in Spain as Bouschart and written in the Netherlands or Flanders as Bosschaert.

The writings of the 'Bisschops and de Donnet', town archivists of the city of Antwerp, also mention Lysbeth van HAUBRAKEN, but she was married with Wouter, son of Diericx. Jacobus is the son of Wouter. We consider this latter theory as probably correct. Bisschops and de Donnet do not mention a Spanish Lord of Boscara.