My teacher before in high school still greets me on my birthday every year for 5 years straight. Messages are platonic though and he does it through private message not on my wall. My other HS teachers don't greet me anymore too.  Now I'm not sure if it's still appropriate for him to do that since it's been years like don't you want me to forget you and also boundaries lol. Also I used to greet him before when he was still teaching our class but now I don't anymore because who remembers birthdays let alone their teacher's. But idk need your opinion because I'm not sure if I need to confront it or brush it off or still reply the next time.