WW's Q applies on-hit effects but is itself not an empowered AA (or AA mod, as I like to call it). It is a lock-on spell like any other lock-on spell, that just also applies on-hit effects.
A spell can be made to apply on-hit effects, this is the same for Ezreal's Q, Gangplank's Q, Fiora's Q, Yasuo's Q, MF's Q, etc etc (yeah as you might've noticed, Riot has a tendency to put offensive spells on Q but off-topic), where all of which are spells that apply on-hit effects. Hell, even WW's own R also does this where while his animation shows him AA'ing at a target, it's actually just animation and in reality the spell is programmed as a CC that when hit does DoT of fixed tick rate that also applies WW's current on-hit effects.
And ofc, spells can not be "blinded", it's a mechanics that only affect AA.
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And if you're concerned about "something not working logically", well get a load of this.
- That would mean Anivia should be immune to freezing effects and all ice related attacks.
- Lee Sin should be immune to blinds.
- Sona should be immune to silence.
- Brand should be immune to all fire attacks, including Ignite.
- Nami shouldn't be able to buy boots just like Cass.
- Kindred should be invincible, or at least impossible to kill.
- And ASol should win the game as soon as he's cast his first Q.
- etc etc etc.
Ofc, game logic doesn't always need to comply with real logic, or else a game would be pretty damn hard to make indeed.
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Not to mention, WW has good nose, you can always pretend he is tracking his opponent with his nose when he's blinded anyway, and that he doesn't AA because he might whiff but biting is less likely to miss for him or something (idk, maybe when blinded, he judges distance better with his face where the nose is, than trying to coordinate his limbs). But ofc, remember that game mechanics are never meant to be 100% logical.