It's entirely possible leaving the cleaning staff the heart-shaped box of candy and saying they are your "favorite valentine" may have been the wrong thing to do. Here is my reasoning on this:
Valentine's Day is a day most people associate with romantic love. However, it can even be a day to express gratitude toward really good friends as well, for those of us who are single.
The cleaning staff would fall into the category of "casual acquaintance", since you have only met them one time and you don't have an established, regular, interpersonal relationship with them. They come and provide a service to you by cleaning your house, but that is the extent of it.
By giving them the heart-shaped boxes of chocolates and the note, they may have felt possibly that this was suggesting more of an interest or interpersonal relationship than what in actuality really exists. Specifically stating "favorite Valentine" implies you like them on a more personal level, or even romantic level. The gift and note could have been confusing for them, since they more than likely view you as a customer they provide a service to, not someone with whom they have an interpersonal relationship. I understand from your post you are, without a doubt, genuinely grateful for the service they provide in cleaning your house for you and helping you out, and you were just attempting to express your gratitude. It's just that the heart-shaped box of chocolates and note are something more appropriate for a significant other, or even a very good friend, on Valentine's Day.
Try not to feel bad or guilty about this. If in some way you are still questioning your actions, I would recommend maybe just talking to them if you happen to see them, or just simply write a note to let them know you were just trying to express gratitude for the help they provide you, just to make your actions totally clear.
Hopefully other members will chime in with their thoughts on this. (((Hugs))) 
