Not sure if it was really 6 km. Remember that the spacecraft would then have been bouncing at nearly escape velocity, so it could also be well possible to be at a nearly-orbital trajectory.
After all, the comet rotates slowly (but almost as fast as orbiting the comet) and the trajectory of Philae had a component to compensate this rotation and land at minimal surface velocity.
So, the bounce could really have taken 2 hours or 1/6th of a rotation of 67P Kevin, but the apogee was much closer to the surface, maybe just a few dozen cm above.