And this is precisely the reason why I didn't want to give a 100% thumbs up to a BTA.
Every so often these "mystery" anemones arrive at the LFS that don't have definitive characteristics. IIRC, the last batch of these were more purple-green in color. Maybe it's an undescribed species (I know that's a long shot)?
Are you able to take a photo of the attachment point? I'm curious to see how the foot spreads out. Granted, my CSB is in a box, and there are times during the day where the foot is spread out quite a bit, though the tentacles are clearly indicative of a BTA.