Anyone who's worked waiting tables knows that this happens occasionally. Sometimes customers can be a little more friendly than we'd ideally like them to be, and they ask us out after they're done with their meal.
A kind note like this is harmless, though. It's a shame whoever left it didn't have the courage to ask their server out directly, but we suppose a written compliment is the next best thing. Sadly, we'll never know if a text was ever sent, or whether a date was made.