My mistake. I've never met a Mexican named Castro. I thought it was more of a Cuban name.
Huh? Spanish names are pretty universal all over Latin America. You are as likely to find a Castro in Mexico as you are to find one in Cuba...or Puerto Rico or Venezuela or Paraguay, etc.
Castro is actually a rather common name-Spanish surnames are the same anyplace the Spanish settled-some surnames are more common in certain areas of Spain-but not so much in the New World. My family name/surname is more common in the Pyrenees than other places in Spain-but it is not uncommon in W/SW Texas and NM.
I had a classmate in high school whose name was Castro, and he was Mexican-American.