Actually, the answer to this and the other question about why the 2nd 720 was too early are the same:
Basically: a too-early held 720 isn't guaranteed. In the vid, the 720 was too early because the opponent could have just held Up and escaped; and Noel can reversal super for the same reason. To do it properly you want to have the 720 flash happen on the frame the neutral tech finishes.
Analyzed: If they are vulnerable to throws on the frame of the 720's super flash, they get grabbed and there's nothing they can do. However, if they are not vulnerable to throws, for example in the middle of a neutral tech, then after that animation finishes it's possible to go straight from that to jumping (also not throwable), or a reversal throw-invin move (Noel's super has full-body autoguard until 9f after the flash, which will guard throws) and avoid having any frames where the 720 could grab you.
It is worth noting that if the opponent neutral techs and holds Up during the tech so they will jump as soon as it is over, there is NO WAY for you to 720 them before they jump, perfectly timed or not. They are going from throw-invin to throw-invin. The same goes for reversal throw-invin moves. The reason it was too early in the video is because the opponent hadn't finished his tech, so he could still have reacted during the super flash, held Up, and escaped. All a perfectly-timed 720 buys you is if they weren't already holding Up, they can't get out.