Advice for my nephew please

Okay. To start my nephew is being raised by my mom and has come to know her as “mom” and my stepfather as “papa”. My stepfather is basically just there not at all involved and pretty much hates the fact that my mom has custody of 4 grandkids. But this has been the same for about 12 years so it’s the norm. Anyway.. my nephew is 15 now and joined the school wrestling team . He wound up quitting he never won a match and he just wasn’t into it anymore I guess. Apparently the coach was calling him a “little bitch” and telling him his father must be so disappointed in him.. all of this in front of other kids in the locker room . I guess after he quit the team. Well my mom heard from my niece this was happening and she called the school reported him and now the shit really hit the fan. He’s being brought in for questioning about bullying kids and my nephew is going to be tourted in school now bc of this. My brother was in the wrestling team and this guy was his mentor so he’s pissed at my mom too. Here’s my question.. is this actually bullying or is this a coach pushing a kid to do better? I don’t know. My nephews father hasn’t been in his life since he was 2 so that part pissed my mom off and that’s pretty much why she called but I don’t think the coach knew that. I don’t know . At first I agreed with my mom but now my nephew is so angry with her and apparently none of this bothered him. What do you guys think? Is this bullying or is it just a coach pushing a kid to do better?