It is common for a Thai boy to say thanks anyways. Even Thais that are well traveled will say it. To them, it simply means thank you. Of course, to us it means thanks, but no thanks. In the process of arranging a date, this miscommunication could be disastrous. Just confirm with him what it is he really means to say, and then politely explain how he has unintentionally given the wrong communication. After all, the last thing you want is for him to loose face.

I will typically say some thing like, “In America, “thanks anyways” is a polite way of saying no. Is this what you are saying to me?” Expect him to quickly assure you it was not what he meant to say. If done gently, he will probably thank you for explaining this nuance.