I think the confusion comes about because here in the US, it's common for a local government to use the same phrase to describe an area where a particular act or item is banned.

So, for example most schools in the US are labeled "drug-free zones" because illegal drugs are prohibited, and also "gun-free zones" to emphasize that weapons are not allowed either.

Also, many in the anti-smoking movement describe an area as a "smoke-free zone" when they mean that smoking is banned there.

So for a moment it almost sounded like kilts were prohibited in your area!