Earlier quoted context omitted.
Hunting and gathering is as old as human beings. It's more difficult in the XXI century but in a large-enough forest (and a natural park that is), you can still do it. https://en.wikipedia.org/wiki/Hunter-gatherer
Hunting and gathering is fine if you have free rein of the land and live in a relatively productive area (for fruits and vegetables). From what I know of NorCal it does not naturally grow stuff you can pick and eat. Also hunting is relatively restricted around national parks and there is no mention of petrov doing it.
And there's plenty of small game to hunt and trap. I don't see that Petrov did this, but I imagine if he was comfortable catching and eating a neighbors duck, he probably took a squirrel or two in his life. The natives would obviously fish, take all kinds of small game, even including rat.