Actually, the article says the report says harm happens at 2x the current recommended fluoridation level.
Keyword possible.
e.g. for a while there was a scare for RF from overhead powerlines causing brain cancer.
Turns out, the issue is the statistics used to try and isolate an effect from a general population sample have bias: plug in any effect, and any grouping factor, and you'll probably observe a doubling of the risk.
This effect was the cause of a whole spate of "X may cause cancer" reports in the 2000s.