Unless they catch the perpetrators, we'll probably never know what the MO was. They don't get into how they identified these people as Hong Kong protesters, since they can just as easily have been fanning the flames in classic black bloc operations style to make the protesters look worse in the media and general public, or to pre-justify an upcoming use of force.

Because that's what I care about.

And I don't think your fact is correct? E.g. this post[0] is not about mainland China.

[0]: https://news.ycombinator.com/item?id=19695854

edit: grammar and add second paragraph and link.

Besides, why is submitting news about HK "shilling for mainland China"? Can you elaborate?

You likely have your own reasons for submitting the news, but it does echo China's official position on the protests - Chinese embassies and news sites have been running stuff claiming the protesters are a violent mob for weeks.