Might be that the books are inconsistent about that, then. That’s definitely the sort of detail that an author might miss, as a world grows more detailed. I’m pretty sure that one of the later books is explicit that “sorcerers” are nonhuman.
There’s also a recent-ish story (the one with the OK Corral) that has a character refer to a human spell-slinger as a “sorcerer”, but that character is only tangentially familiar with magic-users, and might be forgiven for using the wrong term (if in fact it is the wrong term).
But, heck, in the later books Harry himself is no longer a member of the White Council. But he’s still a wizard. Granted that the White Council at that point is back to wanting to kill him and only prevented by him being under Mab’s protection, but he’s still a non-Council wizard for as long as he can survive.