It wasn't a block, it was counters all the way through.
Blocking shaves health off, he would've died.
Countering cancels the damage, but you have to hit the counter at the exact time the blow lands.
Chun-Li's attacks on her special attack faster than you can press buttons, so the Ken player literally had to be about a half a second ahead on his button presses, and still get them all timed properly.