It was a professional tournament (although I think it was in the losers' bracket at that point) and the guy playing Chun Li had the guy playing Ken down to almost zero health. Any hit would take him out and his health was so low that even blocking any super move was still going to knock him out with chip damage.
The guy playing Chun Li knew that, so you see him back off and try to get his super combo going, knowing that any hit from his combo, even if blocked, would end the match. However, when he gets the Super Combo going, the guy playing Ken doesn't block it. Instead he chooses to parry, which means he's perfectly timing a tap forward for each and every one of the Chun Li super kicks. That way, Ken takes no damage, and because each kick is parried, Ken recovers a split second faster than Chun Li, which means at the end of the Chun Li Super Combo, the guy playing Ken unleashes his own Super Combo and gets the K.O.
It is an amazing fighting game maneuver that I don't think I could have managed even when I was at the top of my Street Fighter game back in the day.