Yes, it could be that for you a given advert is irrelevant or not worth your while, but the point he was making is that it won't even be worth it for the advertiser to put out the advertisement because it will be noise for everyone.
However, there is only one kind of noise that is noise for everyone: literal noise.
So long as the spam is about something, it is relevant to someone, and therefore it does not necessarily have zero ROI.
EDIT: The only kind of noise that has no semantic is actual "mathematically pure noise" as the person below commented (/u/dang banned my account so I can't reply)
> However, there is only one kind of noise that is noise for everyone: literal noise.
I feel like you're a bit too literal here. When people talk about noise it doesn't mean mathematically pure noise. A signal-to-noise ratio close to 1 is also colloquially called noise.
"Noise" in context doesn't mean random characters, it means garbage or spam or content not worth your while.