Custom built wheels feel totally different than stock wheels. If you are on stock 2200gram wheels, and rode around on 1600 gram wheels, that will make a huge difference. Add to that if he has foldable tires and you are on wire-bead tires,.... you are probably spinning around on maybe 2 extra pounds of wheel/tire. BIG DIFFERENCE.
The Langster will be stiffer as a framset, the Omniums will be stiffer also. Translate that into a much more direct and "urgent" feeling at the pedals.
Carbon post/bars/stem may smooth things out, but a nice fork and a good wheelset will do more than all three of those things combined. My Langster, Carbon Cranks, Ouzo Pro Fork, Carbon Cobra base bar, Fizik Airone Carbon CX, Thompson post, 1500g handbuilt wheels, blah, blah, blah rides like a COMPLETEY different bike than a stock Langster. Night and day.
If you can, swap wheels with your buddy, and see where that gets you. I would suspect that its more than 1/2 of what you felt.
Most guys won't be able to feel crank stiffness. I know I can't. BB stiffness is more likely what you are feeling between the two. That to me says, the Omniums are nicer, ligher but probably not what you were feeling.
Hope this helps.