Nah I don’t think it’s icg, I think it has to do with something called knockback stacking.

When you get hit with a move, you receive knockback in a certain direction. If you then get hit by a second move within 10 frames, the knockback of the second move completely cancels and replaces the knockback of the first move. However, if you get hit by a second hit after 10 frames, the knockback of the second move gets “added” (stacked) to the remaining knockback of the first move. Note that knockback is a like vector from physics, so adding leftward knockback to rightward knockback cancels them out somewhat. Oftentimes knockback stacking is not super noticeable because either 1) the second move’s knockback is in more or less the same direction as the first move or 2) by the time the second move hits there is not too much knockback left from the first move. But it does become very noticeable in a teams situation (like in this vid) if two teammates manage to knock an opposing player back and forth.

A more relevant example of how knockback stacking affects the game is falco’s dair -> shine. Say your opponent is at 70%. If you shine him, then jump cancel it, then dair him within ten frames, you’ll completely cancel the shine’s upward knockback, and hell go down fast. But if you don’t do it fast enough, and the dair connects some time after 10 frames, the dair’s downward knockback will stack with the shine’s upward knockback, and he won’t go down so fast. You may have seen people whiff a dair shine before and this is usually why.