If someone comes from the belief that others who belong to other races (different from themselves) are not as good/intelligent/moral/worthy of being listened to as people who belong to their own race, they can be described as racist.
If a person is prejudiced, discriminatory or antagonistic towards others of a race different from their own, they can be accurately escribed as racist.
There is an implication of perceived superiority in online anonymous posts by those who think others don't know which forum they're posting on and shouldn't have a say on the British Prime Minister based on their skin colour!