The outer layers of anemone is so thin they. An tear easy. The foot is much tougher so they don't tear as easy. When anemone injured the wound just contracted and heal shortly if the anemone is healthy. You see this when carpets loose tentacles. All you see is a shorter tentacle and the tip color is different. As they heal the feta les elongate and the composition of the skin there com back to normal tin a few days, color of that tentacle normalized.
Stressed and unhealthy anemones are unable to heal anywhere near as quick or at all. The result is the wound get bigger and mesothelial filaments spill out as in the picture above.
These wounds are not likely there before but there now. You did not see it yesterday because it was likely not there, not because you and the LFS missed it.
Your anemone is not at all the same health now as he was when he was at the distributer. He is a lot worst.
Continue treatment and hope for the best. Change 100% of the water daily instead of 50 or 75 percent. As long as your water is good and matched salinity and close temp 100% water change then add new med is much better by far