He did it with the intention of driving away people from the community. Doing things with the intention of weeding out people is well described as harassment.

Some people describe that as improving the signal to noise ratio. A good many, I believe.

Eugine would have had the possibility to respond to Kaj with an apology

Likely he's the hero of his own story, and believes he has nothing to apologize for. Never had that lesson in losing against those with power over you.