I agree. IMO all the small prey animals need a HUGE nerf. things like rabbits, squirrels, rats, etc, should be mostly harmless to things way bigger then they are.
I could see a squirrel who's being hunted by a desperate rat being able to fight it off successfully, as they're in about the same size class, or a rabbit maybe being able to fight off a fox if it's cornered, for the same similar size reasons. But a squirrel being able to do anything to a cougar or a human? Ridiculous. I have a colonist who had to convalesce for over a day due to life threatening injuries dealt at the paws and jaws of a freaking squirrel! She had a cracked jaw from a squirrel paw, WTF?!
A squirrel should be able to cause only MINOR injuries and only with it's bite to much larger creatures then it. The only risk factor of a squirrel bite should be infection or disease. If that cougar got bit by the squirrel before the cougar ate it, and that bite transmitted a deadly disease(eg rabies) to the cougar, then I could see the cougar in the OP's example being fatal, but not because the viscous little squirrel just savaged that poor defenceless cougar that bad.