my ex waved at me on Facebook messenger

A little over a week ago my ex waved at me on Facebook messenger. We broke up 5 months ago and haven’t spoken since. I did not reply to his “wave”. Last night, he added me on Snapchat (he didn’t have a Snapchat when we were dating) and a little bit later waved at me again on Facebook messenger. I did not reply. Any idea why he’s doing this?