I really have no opinion here at all. I just wanted to point out that the fact that it’s no morel season in the UK is no evidence in either direction since the post doesn’t claim that the poisoning was due to morels.
I saw a comparable post the other day about an LLM proposing to mix garlic and oil in a way that would have produced a poisonous fluid, which the author recognized before trying. I found that story, and I find this one, at least plausible.