Why did he text me happy birthday when he has a girlfriend?

I dated this guy for 2 weeks and it was pretty toxic/ended on bad terms since he ghosted me when I confronted him about our situationship. He texted me “hey” 3 months after and liked me on hinge again but I ignored it. 5 months go by and he texted me “hey happy birthday” and I’m so confused cause I don't know how he remembers or knows my bday lol (not social media friends). And also he has a girlfriend now? I’ve def healed from the heartbreak but I chose to ignore it cause that seemed like the right, most logical choice. But why would he even try to happy birthday himself back into my life? Doesn’t make any sense to me…
Why did he text me happy birthday when he has a girlfriend?
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