Different evolutionary paths are definitely a possibility in this case, but I'd have to do an autopsy to be sure. Do you think we'd have time to kludge something together in the medical bay for that?

[Probably not, but it might be fun to try.]

And- I'd assume incompetence, for now. Occam's Razor. If they were professional enough to deliberately make non-fatal hits like this, they'd also have to know that doing so would drastically increase the chances of getting caught and executed themselves. Either way, we're dealing with an amateur.