Why does Yasuo's Windwall stop Vel'koz's E?

there is a projectile to it, believe it or not. Velkoz creates a circle showing where the E will explode, and then he throws it on the ground and it explodes. Yasuo can cut it off with windwall for that reason

The same reason is blocks Q, Q, and Q -- It blocks projectiles that move between their source and the wall.

It's broken. Yas in general is broken, and until riot fixes it, yas will continue to be frequently banned garbage.

tfw you don't know what a projectile is.

Lulu's W is also a projectile