African Dwarf Frog behavior?

Your African Dwarf Frog's behavior is normal. I see no indication that he is an African Clawed Frog another answer has suggested. Two things to remember about ADFs are these frogs have very poor eyesight and they breathe in air from the surface of the water. They won't eat something unless they can smell it, it moves right by their eyes, or they find it by accident. It is possible that when he went to the surface to get air, he gulped in some of the betta food as well and ignored his own food for the simple reason that he didn't yet know it was there. Biting the betta's tail is likely an accident as well. Sometimes what happens is the betta's tail moves right by the frog, so the frog may mistake it for food and latch on, then release when they realize it isn't food. I have had that happen with my ADF's and bettas before, but there is no need to worry as ADFs cannot usually eat the fish and generally leave them alone. I have had bettas and ADFs in the same tanks for many years and never had any real problems with it. However, if the tail biting continues, you may consider separating them. The floating at the surface is normal too as long as he is able to swim down and is not bloated. ADFs love to float at the surface. It is just their way of relaxing and being a bit lazy because they won't have to swim to the top for air if they just stay floating there.