whirling blading back and forth instead of going straight?

I generally play with F1 charts on the screen, i forgot here, and i let a stream in the background, forgot to mute it during the re-record...
Anyway, my point was regarding lag, i don't have any. I'm consistently around 30-50ms. I'll do another video record and include it in my thread in the next minutes.
Edit : Here it's.

It's the first time i play Whirling Blades with that amount of attack speed i think. Last leagues i mostly used Shield Charge (casters).

And yeah i thought of namelocking because it behaves like it was the case (despite not displaying a monster healthbar on top), but since it does it even without any mob, there's more into it.