No, it's where they use footwork to get the swing to connect as early in the animation as possible. The fact that it happens sooner than the weapon's speed would normally dictate makes it much more challenging to block.
Eh, to be fair, you both basically said the same thing. If I'm moving to my left while being on your right and I swing at you with a right swing at the same time you swing at me with a left swing of your own, if you don't properly have your screen positioned directly on me, my swing won't have to go through as many degrees to hit as yours will, thus you should have not used a left swing. Spa ghe tea is pointing out (in a horrible way about an already well known fact) that high PS allows you to hit earlier in your swing arc than you would normally be able to do, while maintaining full damage. So when you pair high damage with hilt slashing, you end up with an even more effective and easier to pull off, hilt slash.
By no means though, are these swings unblockable. Nor do they force you to block twice in a row. You only have to block twice if you made both a footwork mistake and a swing direction mistake. For example, there is no such thing as hilt slashing with two people that are completely stationary, regardless of the swing direction you choose. Edit: It could be possible in theory, but you'd basically have to have a 100 blunt weapon so that you could hit as early as possible in your swing.
