That bit specifically comes from experience with the game. Go back and watch it, Mugen was trapped in the animation. You CAN finish a match off an impact move, then a pin, thats not the issue.
In this instance Trance hit his impact move (frog splash) which he then pinned Mugen off. Mugen used resiliency (his Champions perk) and kicked out. At this point, Trance is more than welcome to pin Mugen again, but he can't win off that pin, as its not an impact move, and looks like he's trying to negate the perk that Mugen has as a champion.
Granted, Jamie had no way of knowing that Mugen used resiliency, which is a fair comment BUT, the fact remains that he didn't win off an impact move, which is against the rules.
The only way you can win directly off a pin (without an impact move) is to use a roll up which is reversible, therefore is a fair "standalone and quick" way to win.
Its a ballache when we have to go through FPR, but the grey areas need addressing. This isn't accusatory, its because nobody actually checked the rules and its the first time this has come up. Every time someone else has used a similar combo, they've released the pin. I completely agree, as a "TV ending" its fine, but we have the rules for a reason. Just because you're a heel, doesn't mean you can break the FPR.