Earlier his brother had worked for Rene d'Anjou, and he, Columbus, sailed on Rene's boats involved in a variety of business ventures, and even war.
Rene had some interesting relatives ~ besides an ancestry filled with French Kings, he was a blood relative (through many sides) of the Kings of England, the Kings of Spain, the Kings of Poland, the Electors of the Holy Roman Empire, etc.
Rene was a good guy to have as your boss. Columbus no doubt found his recommendation the way to open the doors to the French and Spanish courts.
Columbus was born in an age where it was common for nobility to send their children "to the countryside" to reach adulthood ~ they would then return to the Chateaux and fortresses where the ruling class lived well able to survive some really serious communicable diseases.
Of note no one in the then world's most powerful city, Venice, had any children in town.
I suspect Columbus' immediate forbears, his mother and father, had perished and he was fostered by a grandparent or, most likely by a surviving uncle.
Casual adoption was exceedingly common in the ages immediately following the Black Death of the 1300s and folks didn't think twice about it.
What a pear they were.