Youre the first youtuber i see really pointing out that you have to switch back weapon _immediately_ after sword swing. If u stick to the sword it will stop your momentum. Most videos dont really mention that, so i had to find it out myself. But with a little practice its quite easy actually, even on controller with default button layout
You didn't really explain how to do it... This video seemed to be more of a tutorial on how to improve upon the technique for those that already have a general understanding of this "sword skating" mechanic rather than explaining exactly how to perform this.