It's hard to decipher if it's a case of her wishing me happy birthday because "we used to care about eachother, once upon a time" or if its for reasons such as you've stated here.
When she basically dumped me (we weren't in an exclusive relationship) she told me in that
text-conversation how "yes we're good friends but the way you're being right now will push me away more if anything." I was totally clueless at the time and was acting way too panicky and emotional when she was essentially dumping me through text. She "dumped" me more than likely because I had been overpursuing her kind of hard for a few weeks once I sensed her being flakey and pulling away from me.
As I said in my OP, we didnt speak since that conversation. Her birthday came and went a few months later, I didnt reach out. A couple months after that, which was 6 months of no contact, she wished me happy birthday. I don't know if that was her way of keeping me believing that we're still "good friends" or if her attraction/interest for me grew during those 6 months of no contact, so she wished me happy birthday as a way to put her finger in the water, as you suggested. Bluealpha1, and others, your thoughts will continue to be appreciated.