Can't be sure, but i assume that picture shows the foot, which seems to be decomposing in the upper center. Be prepared to pull it out fast. In my experience, not many anemones will completely detach and float around to get from point A to B, although it has been reported. Most will slowly crawl. That foot looks like it has a tear and can't attach.
My RBTA came from the store with a torn foot. I placed it in the crook of some rock and adjusted the flow so to not blow it out. It took about 3 weeks to completely heal, at which point it reattached and moved on its own again. I'm thinking if your is a BTA is may also be fairly bleached, but can't see much of the tentacles. Most BTAs don't have such white feet.