Other forms of hurtful behaviour are often mistaken for bullying. Upsetting and harmful things happen, but not all of them are bullying.
Mutual arguments or disagreements are upsetting, but usually everyone involved wants to solve the problem and there is no power inbalance.
A mutual argument or disagreement is not bullying.
Unless you deliberately and repeatedly try to cause someone distress, exclude them or encourage others to dislike them; not liking someone is not bullying.
Single acts of meanness, spite, conflict, rejection, exclusion, physical harm and emotional agression hurt people and can cause great distress.
However, these things are not examples of bullying unless someone is deliberately and repeatedly doing them to you.