High explosive (i.e. one with a supersonic shock wave) would turn the frame to shrapnel. Your average homebrew psycho would probably only be able to obtain a low explosive such as gunpowder, which would be more likely to blow the seatpost out.Was the bomb in the frame of the bike?
I've only heard of one instance of a bomb being hidden inside a bicycle frame; apparently when detonated it fired the saddle skywards but the bike was still intact apart from this. Bombs in bags or baskets make sense, but a bike isn't necessary for that.
I'm not saying that the security team did anything wrong; I'm trying to work out how a bicycle could be used for such nefarious practices.