When he says "Blink and you'll miss it", TC absolutely means it. This isn't just "oh, quick shot", we're talking like 1 frame where it's visible.
I saw it on the first attempt at watching it on Youtube, and went "oh crap, they weren't kidding", and tried to rapid pause to see the shot again, but it's so fast that you just skip over it. I've only been able to replicate seeing the image once since then.
It's legitimate nonetheless and sneaky of them to toss in such a thing. We can't really make any judgment calls of this thing other than "It's a new Pokemon, and doesn't really resemble anything claimed by the full dex leak" though could just the Dex Leak fails at descriptions, but I digress.
Also, it's posted on Serebii, and they wouldn't put something up there unless they have confirmed it themselves.
www.rpgdl.com The site Meeple argues at for too much of his life!