Hm...ever since I saw that, I've been thinking about it, too.
But, it does KIND OF make sense.
Yes, yes. I know. Magneto. 'Nuff said.
But Colossus was EXTREEEEEEEEEEEEEEEEEEEEEEMELY pissed off and whatnot. And he's already been shown to be so incredibly powerful (chucking a 150-200 foot tall Sentinel high into the air, stopping a speeding train [with dozens of cars] dead in its tracks, lifting and carrying a GINORMOUS submarine, etc.). He was also witnessing Magneto torturing Wolverine, whom Colossus feels very strongly for. So...it kind of makes sense that he might have been able to slowly overpower Magneto.