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.
So relative to our modern diet, maybe your point holds, but the California Floristic Province has plenty of plants to sustain humans. IIRC, the indigenous population density was some of the highest in the world.
(Lived in the area for a long time, but not an expert at all). Did the anthropologist provide any details? I'd love to read their work
It's a bit of a digression, but it's a subject I find interesting and rarely pops up in hacker news. :)