I don't think it's a stupid question, considering I've read it asked here before. I just don't think anyone's sure of the answer.
Here's my take on it: There are over a hundred strains of HPV (
all warts are HPV, btw, regardless of what kind), and different strains like to live in different places on the body. The kinds that like the soles of the feet only live there, genital warts only live in the genital area, etc etc. So, it would seem logical that the warts your bf has on his hands will only grow on hands.
Also, if it were possible for his hand warts to spread to the genitals, don't you think he'd have them there by now?