While at a family funeral, a woman approached my 23 year old DS and said "I heard you just graduated from University. Congratulations." and handed him a hundred dollars. He thanked her. He mentioned it to his dad and me the next day. I think that he should write a thank you note, but he has no idea who gave him the gift, and we couldn't figure it out from his description.
Should I call people and ask if they gave him the gift, or know who did? Or would that just seem like I was hinting that everyone should send a present? Since he is an adult, is it none of my business? As far as he is concerned, he thanked the lady, so nothing else needs to be done. There is a good chance that my curiosity is overtaking my common sense.