Discrimination is prejudiced and unjust treatment of someone based on their ethnicity, race, gender, or sexual ortientation.
So, yes, discrimination is a form of bullying, but not all bullying is discrimination, you know?
Discrimination is a more serious word.
Like, have you ever been threatened with violence because they made fun of your pale skin and glasses? Have you ever been harassed on the street because you had average brown hair and eyes? Have people in public who don’t know you ever harassed you about these things?