I got it from the quote in the article from the author of the NEJM paper. You're correct, but this seems to also happen in maybe 2% of people, and there's a good chance 145C is only needed to be absolutely certain all sugars have 100% broken down. Hotpots might still get rid of most of it at 100C. I'm not a polysaccharine decomposition expert though, even though I know they're very heat-sensitive.

If you're really worried (which you probably don't need to be given it's rarity), mushrooms can't really be overcooked (unless you literally burn them), so nuking them in the microwave with a thin coat of oil or frying them off will help get them to temp if you want to be really certain.

Second source from non-paywalled:

It affects about 2% of people that consume the mushrooms raw or only lightly cooked... in people of all ages, ... more often male than female.
...shiitake dermatitis is not seen with the ingestion of thoroughly cooked at a temperature > 145 C.
- Shiitake flagellate dermatitis