Yeah I've seen the video. Wow.
It wasn't the turret giving the damage, because at no point was the turret actually hitting Kayle. She aggro'ed it for an instant but she went out of range immediately and so the turret was quickly back to hitting creeps.
It was Tahm Kench's tongue somehow still hit Kayle with THAT level of missing aim. Not to mention Tahm's passive proc'ed, hence clearly signalling that it hit for some reason. And yeah it should deserve to at least get a look at.
This reminds me of the Thresh's hook, where before there was a time its hitbox was so broken it literally would hook people even if you can very clearly see that it obviously missed the target by a country mile (Thresh's hook to this day still have his rather ambiguous hitbox, but more tolerable at least). This case is that, just I think far more extreme.