Of course there is no evidence that Cochise isn't exactly what he says he is! This isn't a scientific investigation, it's a story. And I expect a fucking twist in it! I'd expect benevolent superpowerful aliens to save us from an evil alien occupation force in real life
before I'd expect something like that to happen in fiction! It's too good to be true, dammit! Nothing in fiction is ever what it seems!
If I can catch a rerun of the episode, I will, but I distinctly remember Cochise saying "I'm fighting..." in his eloquent speech, not "we". If I'm wrong, fine. I don't commit episodes to memory on the first airing.