He said thank you for not forgetting me.

In fact, I think it's normal, but everyone speaks and expresses in different ways, because everyone's personality is different, so it's nothing strange. It's just that his meaning may be a little vague and make you feel strange. I think so, too. When he said this, he actually expressed two meanings. One, of course, is that he must be polite to you when you greet and care about him, so he says thank you. But later, he said, he didn't forget that I was actually an expression of anti-concern and anti-communication. Maybe he's just joking to make you happy, or maybe he thinks you care about him, which means you still have a good impression on him. So what he said can also make your heart clearer, make you happier, and more importantly, convey to you that he feels good about you. I feel that you may not be that interested in him, so you are a little sensitive. I don't think you will be surprised if you are interested in him that way. Maybe you just want to get in touch with and pay more attention to others out of the concern of your friends, or because you think others are kinder and better, but he doesn't necessarily think so. Maybe he will think that you are interested in him, and it's up to you what to do in the future. If you reply, you can reply some pleasantries in the form of friends first.