So im standing on the same side as yasuo

Windwall blocks projectiles 360 around it and if you step inside (in range of windwall hitbox) it also blocks any projectile created inside that hitbox. Rito cant code well so its hard for them to figure out how to make very narrow hitboxes and how to make them block only from one side, too much for script based game.

riot said they are working on it, in the next patches the ability will be renamed in "windcube"

You got the replay for that?

If the projectile touches the windwall its blocked. Doesnt necessarily need to be passing through it

Walls 101:

https://www.calculatorsoup.com/images/concrete-wall-001-comp.png

He can stand inside it to invalidate all projectile attacks.