Interesting but not really contradictory. The fact that there are physically troops there isn’t all that significant. This Wikipedia suggests they’re not allowed to interfere and that they’re not supposed to support public order. Deploying these troops would be maybe slightly less controversial than new soldiers but still highly frowned upon. Sending Chinese troops to put down protestors would probably rally another third of the city state to the cause.

The garrison troops have yet to interfere in the domestic affairs of Hong Kong, at least directly.

If and when they do, it will be unlikely to end well.