Difficult to tell with those pictures. Anemone do remove waste through their mouths, so it could just be expelling digested food stuffs. The anemone looks extremely deflaited and has an unnatural look to it for a BTA (no noticable tenticles, flat and open mouth). Keep an eye on it.
If it doesn't 'perk' up within the next day i would say it is a definate sign of stress, mine deflates every other evening or so, but perks up during the day.
I've gotta stop being so pessimistic about these anemones, i hope it does really well and with the proper environemnt it should do fine.