From the article:

Chinese slaves in Spain ended up there after being brought to Lisbon in Portugal and sold when they were boys. Tristán de la China was a Chinese who was taken as a slave by the Portuguese, while he was still a boy and in the 1520s was obtained by Cristobál de Haro in Lisbon, and taken to live in Seville and Valladolid. He was paid for his service as a translator on the 1525 Loaísa expedition,during which he was still an adolescent. The survivors, including Tristan, were shipwrecked for a decade until 1537 when they were brought back by a Portuguese ship to Lisbon. There are records of Chinese slaves in Lisbon as early as 1540. According to modern historians, the first known visit of a Chinese person to Europe dates to 1540 (or soon after), when a Chinese scholar, apparently enslaved by Portuguese raiders somewhere on the southern China coast, was brought to Portugal. Purchased by João de Barros, he worked with the Portuguese historian on translating Chinese texts into Portuguese.

Chinese boys were kidnapped from Macau and sold as slaves in Lisbon while they were still children. Brazil imported some of Lisbon's Chinese slaves. Fillippo Sassetti saw some Chinese and Japanese slaves in Lisbon among the large slave community in 1578, although most of the slaves were blacks. Brazil and Portugal were both recipients of Chinese slaves bought by Portuguese.