Marvel is taking the position that mutants are not humans at all. But this isn’t an ideological or a moral stance. Instead, it is a financial one. Toys manufactured in other countries and imported into the US are subject to taxes, but those taxes are lower if the toys represent non-human characters. That has led to Marvel lawyers arguing that an action figure representing, say, Wolverine, is actually “representing animals or other non-human creatures (for example, robots and monsters).”
It seems the classic question of human or mutant now lies in the hands of the IRS.