A, No way do I believe a 21 whp gain from an CAI, that would be about 25-27 fwhp gain (unless the stock filter was full of dirt)
B, Dyno numbers can be manipulated
C, They made the pull in 3rd gear which isn't 1:1 . The pull should have been done in 6th or in whatever gear was 1:1 and not being mechanically multiplied
CAI's typically do flow far more air vs a stock intake, the real gains only present if the engine actually needs more air and unless you've done heads or a cam or both, it doesn't.
Also, the gains are typically "peak" numbers only or at the end of the RPM where they are of no real benefit. Example, say at 6000 rpm and the factory air box starts to suffer and costs 10hp vs an aftermarket CAI that flows well and at the same 6000 rpm the engine doesn't lose power but at 6300 starts to nose over. The "gains" are measured there vs throughout the RPM range where the differences would be maybe 1-2 hp which could be a variance between pulls.