I don't know, but I suspect it's because Chinese Internet Mobs like to use it as a BBS bandwidth destroying soapbox for stuff that nobody cares about.
that video is no longer available man. I heard that video is falsely edited as well (but then.. it's from the korean side)
Well.. I don't wanna see waves of 10,000 red communist flag in my city for sure. Especially when the flag really symbolizes communism... I will bring both US and Korean flag for sure. It would be a disrespect to US to bring Korean flag alone when I'm a US citizen.
I do not know you and there is not reason for me to doubt what you have said. However, base on my own knowlege about Korean, I beleive the vast majority of them would just bring Korean flags given the situiation we talk about. And I would not blame them doing that, nor would I have any ill feeling towards it.