Actually rolling off the throttle mid corner will make the bike run wider, and a bit more will help tighten a corner. This is of course predicated on the assumption you aren't already at the limit of traction. Watch twist of the wrist 2 for a more in depth example.
I don't have time right now to watch this video but I think you have it backwards. Keep in mind that if you accelerate the bike will go faster and require more lean angle to maintain a steady turn. If you decelerate then keeping the same lean angle will cause your line to tighten up. There are a few other factors that complicate all this. For one, when you roll into a curve you need some additional throttle just to maintain a constant speed since the edges of tires have a smaller circumference than the middle of the tire. Second, depending on chassis geometry and tires, chopping the throttle
MAY cause the bike to want to stand up and run wide. I would guess that if your bike tends to stand up under braking it might also want to stand up if you chop the throttle. Regardless, if you slow down you can tighten your line with proper steering inputs.
Here's a quote from an article on cornering as well as the link to the entire article:
"Note that acceleration typically makes the bike drift wide and deceleration can either cause the bike to drop into the corner more or cause it to stand up, depending on how abruptly the throttle is chopped and how the machine /tire combo responds to this input."
http://www.ridinginthezone.com/how-not-to-suck-at-cornering/Regardless, if you are going into a curve too hot, rolling on the throttle is NOT the best way to make it around the curve.
I did take the California Superbike school. Keith code did recommend rolling on the throttle as the fastest way around a curve but he was assuming that you slowed down enough before the curve to be able to do this. Also there are plenty of racers who don't agree with this technique and trail brake into the curve and roll on the throttle once past the apex as they start to stand up the bike and accelerate out of the curve.