Don't need to go back 20 years.
Only two years ago, PLA was formally requested to assist in disaster relief by Macau regional government.
Garrison was deployed in "combat" uniform, which showed confidence in local support.
This might seem like a small detail, but it is not. Not sure where these decisions are made in the PLA chain of command, but usually a local commanding officer can dictate "dress of the day". If they had felt combat uniform would send a bad message, they can authorize PT gear like sweats.
In HK, standard orders are for any military uniform not to be worn outside of barracks unless for some kind of event. This is pretty extreme, as it is pretty typical for any military personnel to go out in uniform to make a coffee run or some other thing like that. However, since PLA presence is so sensitive for some HK people, they are obviously erring on the side of caution.