Hired thugs? I assume you mean in Yuen Long right? Here is my question, do you know where Yuen Long is? It's quite far out of the city of Hong Kong (I mean the name has far in it). So the story goes that the "protesters" went there to do what exactly, and then got beaten up right? So why were they so far out in the first place? Since it's quite far out of the city center, do you really think someone can quickly pay thugs to create a coordinated attack against these rioters when it was sort of a spur-of-the-moment type of thing?
Personally, I am more convinced that the "protesters" are the agitators of all of these, you are more than welcome to show me otherwise.
As for violent police, the UK deals with protests are even worse, but I've not seen escalation to this sort of level.