>and yes even "see you later".

this being my point. how do you know that what you were hearing wasn't someone saying thanks as they were leaving?

I think you’re right. You do (or, at least, when I imagine it in my head, I do) hear it frequently used when saying goodbye, but I don’t think it would be used to say goodbye.

If someone said ‘cheers’ to me when parting, I’d interpret it the same way as if they’d said ‘thanks’ — which could be slightly strange, depending on the situation.