Boy fights back against a bully

There is a comment below the video, is it correct?

The larger kid was a known bully at the school, and the smaller one was finally standing up to him...That is why it was being recorded.

The narrative in the story never clearly identifies the "bully" or the "bullied". I think we assume the fat kid is in the roll of the "bullied". I know when I was in school the fat kids were always being picked on.