Helping son's homework

Today, I helped my son with his homework. He was quite annoyed because he was very tired, but he had to finish his homework either today or tomorrow, or else he wouldn't have time to do it.

He didn't have any reason to be mad at me, but I'm not sure why he was a bit upset with me while he was doing his homework. It was starting to annoy me, but I kept my feelings hidden and continued to help.