Feeling Crushed & Confused

So me and my ex broke up about 5 or 6 months ago, we were together for 3 years. He started dating someone quickly after like about a month or 2 after we broke up. He told me he missed me and will always love me etc etc when we spoke briefly but then we went No contact strictly afterwards when he blocked me. I realize now that he blocked me because he is in a relationship. Anyways, he texted me happy birthday with all the emojis and the imessage celebration effect. I was confused bc i thought I was blocked. Anyways all i said was "Thank you!!" he said "no problem" with an emoji and i just left it on read. Why does this feel hot and cold? But then again why wish me a happy birthday if you blocked me before and you're in a new relationship?