This made me feel bad. Any thoughts?

So yesterday was my daughter Kimberlys 8th birthday and because my wife is on a business trip, I went to my daughter's school and ate lunch with her. She has a group of friends that I know somewhat decently (they were all going to see beauty and the beast that evening). I saw that the school was selling these GIANT (I mean absolutely massive) chocolate chip cookies. Well I gave each of the girls 2 dollars to go and buy a cookie (No worries, my wife and their mom's are friends). A few minutes later, they all came bag and dug in to their enormous treats. Then this really overweight kid comes over and asks my daughter for a piece of his cookie. Apparently his name was Hopper and he was mean to the girls, but I didn't find out about that until later. I'm thinking that Hopper is one of her friends, but Kimberly said no. She said it politely too. Hopper then tells me to make Kimberly give him a piece of her cookie. I told him that it was her birthday, and it was her special treat and gave him 2 dollars to get his own. The other girls laughed and he went to buy a cookie. A few munching minutes later, hopper comes back and asks Kimberlys friend Sara Bell for a piece of her cookie. Sara said no and laughed. Hopper then asked me to force Sara Bell to give him a piece. I said that it was Sara's cookie because she was celebrating Kimberlys birthday. He then GETS MAD at me and tells me that he should be celebrating too. My patience was starting to go away. I told him that I had already givin him money, and that he already had a cookie. He then goes and gets a teacher, who I guess was his mother. Kimberly started crying. Hoppers mom told me that I was being unfair because I gave the other girls cookies and only bought one for Hopper. I then ended up giving hopper 4 more dollars to get two more cookies. Kimberly was devastated. I feel bad. Any thoughts?