I think you're right.
I don't remember Amber claiming she was diagnosed with BED. What I do remember is that she claimed to had been diagnosed as bipolar as a teen.
This whole debacle shows how out of touch with reality Amber is (and how she thinks that being 500+lb is no big deal).
Sure, she pulled that number from her ass, but who, in their right mind, would come up with such a huge number? Amber really thinks it isn't that abnormal to weight more than 500lb.
Tbh, what Tammie did was crazy, and invasive of Amber's privacy. She had absolutely no right to do that (spare me with the worried aunt shtick. If she was such a caring person, she'd have taken Amber in when she was taken from her parents.)