Bullying is not just being mean
The "Bully" is often a victim of poor examples. Kids are not born bullies. They are formed into them. These examples can be from other students, siblings, parents or adults in their lives and yes even their teachers. When a child witnesses adults saying unkind things about or to others they get the idea it is ok. They repeat this action, when a child is mistreated by a peer they react in kind to someone else. What we see or experience we repeat. It is simple sociology. Bullies can be victims.
Peers are often the biggest bullies in a child's life. We make excuses for others treating us poorly because any attention sometimes is better than no attention. Kids are especially vulnerable to this because they a so desperate to be included they will suffer mistreatment.
Boys are typically more physical bullies (threats, physical aggression) Girls tend to be more social bullies (secrets, exclusion) This is not 100% but my experience and research shows this to be the case.
Most reported bullying is not bullying. Plain and simple the understanding of what bullying is tends to be the problem. Bullying is a systemic and intentional long term mistreatment of another individual. Telling someone that you do not want to be friends with them does not make you a bully, not sharing a snack does not make you a bully, not picking someone in a sports event in the order they want does not make you a bully. A bully targets someone with the intention of causing them harm either psychologically or physically. They do this more than once or twice, it is calculated and intentional. Most cases of "bullying" do not fit the actual description.
Just because it is not bullying doesn't mean it doesn't matter. As adults we should listen to all complaints of bullying and then take a moment to educate and assist. It is our job as adults to help kids navigate these trials. Especially because if we don't they are going to turn into those adults that whisper around the corner and make you feel like crap because they learned they can get away with it.