At this point you should go and look up what 4K video is. This is quite impressive stuff and (I presume) is a differentiator vs the 2016 MacBook without Kaby Lake's video support.
Errr.. The point is we don't actually know the specs of the videos edited, aside from the resolution.
It should also be noted that Kaby Lake's new hardware video support probably applies to
none of these videos, as there is currently no support for it in macOS. The support is only available in High Sierra.
EDIT:
So the 1st 4K video is from a Galaxy S6, probably 2160p30 h.264. So hardly surprising. Indeed, the guys said the 2016 MacBook handled 4K fine too, which I assume is the same type of 2160p30 h.264.