I second potential Aiptasia and taking the rock out, but I can't recommend scraping it off. Tiny bits of pedal tissue are enough for it to fully recover. If loose bits start floating through your tank you will be greeted with more of these guys soon.
Take it out, treat the rock appropriately to fully dissolve the anemone, and only after it is fully gone and you rinsed the spot thoroughly + brushed it clean, I would return it. Kalkpaste, AiptasiaX, Aip-Away, and similar products do a decent job dissolving these anemones, but treatment outside the tank is far safer than inside.