A human embryo is human regardless of whether we’re talking about other species or not. So is a human corpse. I’ve also seen people say an embryo, egg, etc. isn’t alive, which is patently false; they can die, so they’re alive. Nonhuman beings can’t be people, and nonliving things can’t be people, but being human and being alive aren’t the traits that matter, except as they relate to being a person.
That’s why I’m suggesting “not a person” is the right language to use, because we’re talking about the concept of personhood, which is what we use to distinguish entities with rights from those without.