Seamless transitions
Playing the video at 1/4 speed on YouTube, there's no discernible transition other than a hard cut.  If there were some sort of cross-fade or dip-to-black or luma fade, it should be visible at that speed.  And it's not.

I suspect that part of what makes the hard cut transition successful in that video is that the motion and the balance of the center of interest in the "from" clip leads the eye perfectly to the center of interest in the "to" clip.  Hard transitions look harsh when the eye must find and acquire a subject in a different part of the frame across the cut.  If the eye is already properly aimed and focused, the hard cut just looks like a seamless transition.