No underwear

My son is now 7. When he was 5 he was outside with his dad. Somehow a conversation started between my husband and another tenant from the building. She was really tall about 6 feet and was wearing a short skirt. My son is very friendly and ran up and was talking to her. She was talking to him and he went to hug her legs. My husband said our son got a strange look on his face and looked over at him. My husband asked him what was wrong and our son says "Daddy why isn't she wearing underwear?"
My husband said the girl went about 6 shades of red and quickly took off and he was trying not to laugh. I ran into her a couple of days later during a fire alarm and was wondering why she was pointing at my son and whispering to her friend.