He skipped cutscenes and went back to watch them.
Side Note: When was Proud Mode suddenly hard? Proud Mode isn't that hard if you've been playing KH for quite some time now.
Yeah, if you're a veteran KH player, that should actually be what you're usually playing on (in my opinion). I always go right to Proud Mode, Critical if it's readily available in my first playthrough.
And 30 hours is around the standard for a KH game, so people shouldn't be freaking out. Nier Automata is 30 hours, and the story is great. Kingdom Hearts games have never been super long to beat, and since we know that he skipped the cutscenes... 30 hours is him just blitzing through. If you're watching everything and playing it how it's meant to be played, it probably goes up about, maybe 32-33 hours. It depends on how much he actually skipped.
If he skipped damn near 90% of the cutscenes in the game (which I doubt, but who knows?), it's possible that the game COULD get up to 35 hours, possibly higher.
Again though, people shouldn't think Game Duration = Story Quality, because those two don't correlate. The only thing it indicates is how long it takes the player to beat the game, that's it.