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)