I need advice...why might he have messaged me?

I decided to follow my ex on instagram about 2 days ago and I liked his picture and he liked mine. We did end in good terms and we ended cos he didn't have time for a relationship and he just kept ignoring me. I know he isn't interested in me like that I can tell. I don't want to be in a a relationship anyway.

Now it's 12.30am night time.

He messaged me on instagram first today saying "hey bighead" at 6am and he sent my instagram picture to me not screenshot but just my account picture to me. I replied at 2.50pm in the afternoon saying "oh hi😂" He's not seen that message yet and hasn't got back to me yet. Been over 9hrs. We never dirty talked even when we were together so it wasn't and isn't like that. I just miss him.

I did get back in contact with him last year and he showed interest in me for abit and then lost interest then ignored me. I deleted him off my life.

I wasn't going to message him anyway when I added him on instagram but don't get it why he had to message me first