Fluoride rapidly forms a highly insoluble calcium fluoride salt. So you won't find a lot of it in blood or other easily accessible body fluids.

Regardless of where they got the list (edit: which I do think is a fair question)...

> the first link [...] doesn't seem in favor of this?

To me that falls under "the best evidence [available] in favor of this." It's not great, but it's not nothing; it's certainly something in favor. After all.. I guess I don't know about you, but I feel like if someone told me dose X of something is toxic, I would not feel comfortable feeding myself and the entire country 50% of that dose, on that basis alone.