These are mollusca. Mollusca develop a dimple, which is more noticeable when they are frozen, just as the doctor said. Despite their name, mollusca are most often not contagiosa, and are not contracted from anyone--they just happen. Kids get them often. They have no cancerous implications, as regular HPV warts sometimes do.
Save the vinegar for the salad, have the doctor finish off the mollusca, and don't worry.
Best.
Dr. Rockoff