It is hard to believe that anyone let a lone a scientist would believe that any human would be that specialized in their diet.
Humans naturally are omnivores. They crave a varied diet.
As far as protein goes for a hunter gatherer society, yes you would take advantage of dependable salmon runs for your protein.
But you are also going to gather nuts, grains and fruits. You are also going to dig for tubers and other root vegetables.
There is not going to be any available food in your area that you are not going to utilize.
There is an area near where I live called Indian Heaven. Lots of huckleberry fields and camas lilies grow wild (natives ate the roots). And historically wild salmon was plentiful.
I don’t see how anybody would overlook berries - delicious and plentiful.
There had to some source of vitamin C, to prevent scurvy.
Vegetarian: Old Indian word meaning “Cannot Hunt or Fish”...............