I'm pretty sure smart labels is opt-in, so it's more fair to say that it's the result of a filtering feature the user turned on but does not explicitly control and cannot accurately predict.

It's usually very reliable, so it's easy to forget that it can mislabel an important message as a generic promotion.

The subject line seems a little too much like a generic promotion...

Smart labels is an option in 'Labs', disabled by default.

You don't create a specific "Promotions" label though. My answer to brown9-2's question is still correct.