RBTA can stand for Rose Bubble Tip Anemone or Red Bubble Tip anemone. I don't think there is any distinction.
A lot of the "ultra" RBTA like Sexy corals are just interesting morphs that show up, but they are still almost identical in care to other RBTA. Probably only one of those show up for every 200 a wholesaler gets or more. I got ONE rainbow RBTA in my entire time at Reefworks, if that tells you anything...