Would we possibly have a wrongful termination case?

My husband was fired from his job as a high school coach. In his employee manual it's stated they when they do something wrong first time is a warning, second time is a coaching (basically a talking to that you sign but does not go in record.) next time is a write up. You get 3 write ups in a year it can become termination. They skipped ALL that because in 7 years working there he has never gotten in trouble and jumped straight to firing him. How he got fired was because there is an 8th grader that it's a common joke around the school, has a crush on the librarian. It's because he has no friends and only ever talks to the school librarian and helps out in the library. So everyone even the teachers thinks he has a crush on her. My husband pulled a joke when he saw him in the library helping put books away. He poked his head in. Said "Alex! I'll by you 5 minutes with her!" Shut off the lights and closed the door. It was stupid and immature. I even told my husband that he's a grown man. And why was he doing that. But the librarian freaked out and was crying. She for some reason thought this was a plan for the 8th grader to SA her. She told the principal and my husband didn't even get a write up. He was fired. His joke was dumb. Immature. But they could have written him up instead of firing him and my husband made a point that if she thought the 8th grader was capable of SA then why let him help out in the library even when no one is around? If they didn't follow their own rules is this wrongful termination?