AITA for not punishing my son for making fun of his sister for wetting her pants?

My husband 40m and I 38f have two amazing kids 10m and 7f.

Our sons birthday was a couple days ago and the gift he was most excited to receive was the video game Dying light, he heard about it from a friend and was really excited to try it out. It’s a video game about zombies and he loves anything zombie related.

Today he was playing the game in our living room when his sister came downstairs and unfortunately she walked in during a pretty scary part, this part of the video game scared her so bad that she peed her pants.

When her brother saw that she had peed her pants he started laughing at her and said ” ha ha you peed yourself your a big baby “.

I went in and asked what was the matter and saw that my daughter had wet herself, I asked her what happened and she said that there were scary monsters in the video game her brother was playing and they were so scary and she started to cry.

I then comforted her and took her upstairs to calm her down.

Later my husband came home from running an errand and asked what our daughter was so upset about, I explained what happened to him and he asked what punishment I gave our son, I told him I didn’t punish him. This made my husband very upset, he asked why I thought it was okay for our son to bully his sister, I said i didn’t think it was a big deal but he insisted otherwise.

My husband has been very upset with me since and claims that I should’ve punished our son right then but now since I didn’t he will look like the bad guy if he punishes him for making fun of his sister after I did nothing.