Actually, back when Taiwan insisted calling itself the “Free China”, pulling stunts like this gets you pretty dead.
In “Free Taiwan”, after the 1996 presidential election, this kind of stuff is tolerated. Mostly because the people driving the Chinese flags around used to be the same people that would get you pretty dead.
I think they are connected with this organization:
In their website, there is a page dedicated to naming all “pro-Taiwanese independence” people, so that when Taiwan is united with China, they can be tried for violating the “Anti-Separatist Law” of China.
For some reason, several professional baseball players, such as 張泰山 (Chang Tai-shan) of Eda Rhinos, are also on that list… wonder what they did to deserve such attention from these nutjobs.