do you think the teenager Joshua Wong Chi-fung got involved again with this violence? ... how is he anyway? has he finished his Uni yet?
Neither Joshua Wong nor his affiliated groups have anything to do with these riots. The fringe activist group involved here is Hong Kong Indigenous which wants independence for Hong Kong (as in becoming its own country) and wants to preserve its unique characteristics (as in a romanticized and whitewashed version of what it was under British rule in the late 1900's).
A related note is that illegal street vendors tend to have to pay protection money to organized crime, so removing illegal street vendors would be a direct hit on organized crime income. The area where this happened is an extremely densely populated, low income neighborhood which is a longtime hotbed for organized crime rackets. The police is investigating whether the riots may have been pre-meditated.
My personal view is that this may have been a mini perfect storm. The Hong Kong police ultimately kept it under control despite initially being caught by surprise then maintaining maximal restraint throughout. As most of the population and most of the city's political spectrum have condemned the riots this incident should not take too much of a toll on the police force's morale. I think it would help morale as well as be prudent for the police brass to make sure they have the capability and willingness to deploy large enough numbers of riot police on very short notice, and let it be known throughout its ranks.