No, I think the 'Reds' that come after the 'Blacks' are in fact people who break off from the 'Reds' left flank. If you look on the ground you will notice that the majority of routers 'cut down' are 'Reds'.
I really doubt the 'Reds' outflanked the 'Blacks' as they were clearly outnumbered and in a much denser group (which was why they could push the 'Blacks' right back). Also take note that 10-15 seconds prior to the break you see 'Reds' from their right flank break off and flee. Clearly that flank was being pushed far more than they could take.

And I agree, I could easily imagine two TW players controling these guys, frantically clicking to charge, reform and flank. Too bad they were Impetuous and Undisciplined.

They are throwing stuff, but mostly they are lobbing flares at each other. Dangerous if you get it in your hair or under your shirt/jacket, but as you can see it will just drop to the ground mostly.

I find this little clip hugely interesting as you can see, but at the same time I dispise the act. I guess I allow myself to be interested as it is two groups who wanted it and were stupid enough to do it, thus letting me analyze it rationally.