I can see pretty clearly in that vid that you hit it on a later active frame. You did it pretty far away from him after the blocked st. mp and had he not pressed anything it most likely wouldn’t have connected at all (even for blockstun). What he did was extend his hurtbox by pressing something and ran into your cr. mk later while it was still active granting you +7/+8. This is something the normal counterhit setting in training mode doesn’t take into account, but you can replicate the situation by recording either Chun Li attacking you in that pattern or the opponent sticking something out into your cr. mk (for a more legit, spaced counterhit).
Those later active frame jab into sweep spacing tricks people are talking about are usually due to the opponents hit-reel animation causing the first active frame to whiff from a certain distance (but not the 2nd active frame).
Another move I’ve been playing around with for active frames is cr. mp. It’s listed as 0 frame advantage on hit, HOWEVER when used as a spacing tool (something the opponent’s gonna walk into or stick out a normal with a worse hitbox) or used as an anti air, it almost never connects on the 1st active frame (it has 5), meaning 9 times out of 10 you can link it into the mk version of super (that’s right… an anti-air super!). I’ve been doing this for a few days now and it works like a charm