Hi Vixen
I couldn't open the picture of yours on my computer, but if its hands look like little mittens, and it looks like the one on the other thread, it is an ADF.
I'm having trouble with my mouse today and so am a little slow responding to posts, but I think I recall seeing somewhere that you have 3 frogs in a small tank with corys and a betta? If that was yours, your problem might be due to overcrowding.
I prefer to keep them by themselves, mostly because they are the ones that need protection, but once in a while they nip fish. This is usually an accident because they tend to be shy little creatures. The thing with frogs is that they snap at anything that passes their field of vision at the wrong time. It's a reflex only. They do not stalk their prey or anything like that. Therefore, in a bigger tank, the chances of this happening are greatly reduced.
Also, they usually swallow their food whole, so the idea of eating a betta just does not seem practical.
On the other hand, if he were an ACF, I would start to worry.