As a Hongkonger, I never wonder why there are so many "Vietnameses" using English and try their best to infuriate Chineses.
Their goal is to deteriorate the relationship between Vietnam and China. If two countries go into war, they will even get very happy!
Those "Vietnameses" were refugees forced to leave Vietnam (from South Vietnam), in both political and economic reason. Growing in the 80s and 90s period, I have seen so many of those in Hong Kong acting very aggressively.
In their minds both countries are their enemy. They even welcome a ruined Vietnam to prove that their departure from Vietnam were justified and unregrettable
Hongkong people would like to be part of Britain. Who must get out from Hongkong ?