Can an alley cat really kill a lv0 commoner?

A real cat can kill a grown human. Have you ever seen one flip the fuck out?human stands no chance.

My cat nearly killed my ex-wife with one bite, once. (Not immediately, but cat bites tend to carry infection, and if the infection reaches the bloodstream, it can. That combined with hours having to wait in an emergency room, and . . . a person could die.)

D&D rules-as-written tend to be very unrealistic, which is one of the reasons I play TFT or GURPS or other games that have more reasonable rules that represent situations and outcomes better.

(As for your “who would win” tag, what usually really happens, in human vs cat combat, of course, is the cat runs away and escapes. The cat counts that as a win. Human opinions vary.)