From your own quote,

They evolve from discriminatory grounds, and have an effect of nullifying or impairing a person from benefiting their rights. When these behaviors become repetitive, they are defined as bullying.

Downvoting someone because you disagree with their opinion is discriminatory.

Reducing someone's rep below zero has the effect of nullifying or impairing a person's voice (free-speech).

When these behaviors become repetitive, they are defined as bullying.