Not trying to be a wise-guy here, but I've done alot of taxiboosting and those seem totally fine to me. I've gotten more height than that by boosting less than that
If he had something like three very fast consecutive taps to boost the first wall, I believe the outcome would look something like that.
I think he's clean anyway, boosts can look a little floaty sometimes.
[noembed]http://vimeo.com/6881103[/noembed] 0:38 in this vid is a great example of a clean taxi-boost that looks modded