I looked at the wiki page someone linked and it took until 1980s for a scientist to link the mushroom to a specific antigen it had, and was only labeled as poisonous in most cookbooks by the 90s.
You forgot to account for the fact that people are fucking morons.
Despite the poisonings, Paxillus involutus is still consumed in parts of Poland, Russia, and Ukraine, where people die from it every year.[71][72][73][74
I looked at the wiki page someone linked and it took until 1980s for a scientist to link the mushroom to a specific antigen it had, and was only labeled as poisonous in most cookbooks by the 90s.
So the story could be believable
You forgot to account for the fact that people are fucking morons.
Wikipedia.
Well can’t fix that, just like you can’t fix random people trying to get in the worst caves in existence