Hi Daffy!
While SLASH animations cover a wider angle (matching the SE, SW, NE, NW ranges), the THRUST and SWING animations play orthogonally, being directly oriented towards N, S, E, W.
Think of them as a different type of attack. In terms of gameplay, slash attacks could be wider (they can impact enemies on a wider angle), while thrust attacks will need to be precisely placed to impact the enemy (probably dealing more serious damage).
Your assumptions about animation directions are right; most character animations in the collection follow the SE-SW-NE-NW logic. However, for some attacks, such as the ones involving spears or ranged weapons, you will find this alternative N, S, E, W directions.
I hope it makes a bit more sense now :) Anyway, if you have more questions, feel free to ask.
Have a nice week!