Im not a 767 pilot, but I think I can say with confidence that the 767 can handle turbulence with no problem. All transport category aircraft are designed and tested for such things.

A buddy of mine has done a bit of flying over the north atlantic and explained to me that turbulence over the pond, and getting away from it to find smoother air is a different ball game than when you are in radar coverage. Over the ocean, there is no radar. Pilots instead make position reports and controllers use non-radar procedures to keep aircraft separated. Very often this means requests for altitude changes cannot be granted, even if the ride is really bad like the one you described. There are ALOT of aircraft crossing the atlantic on a daily basis.

Finally, the guys may have seemed like it was nothing, because to them, maybe it was. Turbulence is just a given in what we do...comes with the territory. Personally, I don't always find it enjoyable, particularly when it gets really rough. But up front, we can see the big picture and can control the airplane. So long as its able to maintain its altitude and speed and stay right side up, there really isn't much to be worried about...stay seated with your seat belt fastened like the F/A's tell you and you'll be fine.