Pyro said:
Gohan sounded like he was just now realizing Goku and Vegeta were fighting at a level above normal Super Saiyan when he talked to Kaioshin, so I don't think he suspected they had Super Saiyan 2 beforehand. It's really sloppy writing because it makes all the characters look confident and retarded simultaneously.
I think he does but he just didn't expect the spower of SSJ2 Goku/Vegeta being stronger than his CG counterpart since Goku told him that he's the strongest.
Let's not forget about this as well.
Chapter: 426 (DBZ 232), P4.2-3
Vegeta: “At that time there was a large gap between our powers…But what about now? While you’ve been enjoying peace, I’ve continued to train.”
Chapter: 452 (DBZ 258), P1.1-4
Goku: “Gohan, it’s your turn next, but have you trained properly?”
Vegeta: “Unfortunately, it seems he got carried away in peace and didn’t do any significant training. Our powers are higher than his now…Though I suppose there’s no telling what would happen if he snapped and went into a frenzy… ”
Kaioshin: “S-so that’s why these 3 have such composure...In a pinch, they can put forth tremendous power, like Son Goku displayed momentarily…”
Gohan needs to turn Enrage SSjin2 in order to surpass Goku/Vegeta.