Again, it's not even his article. I'm just tossing that whole line in the rubbish bin on that basis.
And yes, Ngo has made it his M.O. to document antifa behavior. It's not unusual for a journalist to focus on a specific issue. Let me ask you if there would be any caveats to be found in an article if a journalist who spent years documenting right-wing hate groups were to be attacked. I can assure you, that there would be no "he was looking for it" type of moral equivalence.
That specific article is not his article, however he did vouch for it, vocally support it, and agree with the ideas behind it.
As for the documentation of antifa, I think it is impossible to be a solely anti-antifa journalist when almost every single one of these incidents (including this one) involve counterprotests against violent far-right hate groups. In focusing exclusively on the evils of antifa, you create a narrative which indicates that those right wing hate groups are innocent victims (which obviously isn't the case) and that silence condones those hate groups who were just there to wave their flags and be peaceful, right? (that last bit was sarcasm...)
That said, I think you could very much have an individual or group who was anti-right wing who went into right wing protests to start trouble and I think that they would get criticized for "looking for it". In fact, you might be able to put many members of antifa in this very category. Some individuals go to these protests in order to encourage the other side to cross a line so they can use it for their narrative. Again, condemn those who step over the line, but watch for how this information all plays into the larger narratives. Like, consider the fact that you don't see a widespread story like this every time an antifa member or a Proud Boy gets punched in the face. Why is that?