I think the gp is disqualifying Stamets as an authority because he makes claims that are poorly supported by evidence. I agree with this assessment. He also happens to have no formal qualifications. So from where does he derive his authority? And if he has no authority, why is an article that is based on his authority interesting? I agree with gp that he's interesting, but he's also a salesman for fungi --- literally.
For example, he sells lions mane extracts which promise to improve memory and cognitive function. All of the science in this area is based on mouse studies. Stamets asserts this "translates from mice to humans," and leaves it at that. He makes statements such as "a Japanese researcher postulated" or "there are several clinical trials out there" (without commenting on their design or even conclusions). So while nothing he says is a lie, everything he says is meant to point to a certain conclusion despite a dramatic lack of direct evidence. If lions mane really helped that much, you'd think it would be easy to determine that, because given it's safety profile it should be easy to run a study on humans.