You're sort of right. If he'd said "we have zero tolerance for anyone going over 10 mph," it certainly wouldn't have been as funny. Instead, he proclaimed proudly that "we have a zero tolerance policy" and then explained it only applied to people going 10+ mph over the limit in the next sentence.

There's a difference between using the phrase "zero tolerance" to describe what happens in a certain situation and using the phrase "zero tolerance" to describe your policy when it has tolerance built into it.

(I un-downvoted your first post)

So now the limit is effectively 10mph faster than what is actually posted.

New policy: All crime is now illegal.

And is that policy billed as a "zero tolerance for drinking and driving policy" or a "zero tolerance for drunk driving" policy?

There is a law against drunk driving that mentions a 0.08 threshold. There is a law against speeding that doesn't mention 10mph leeway.