It sounds like he’s trying to open the door to getting back together with you. Maybe he thinks that claiming “friendship” is the way to do it. I bet his current squeeze isn’t working out, and he doesn’t want to be alone. He’s hoping to get back together with you - but only until “someone better” comes along.
I admit I’m suspicious by nature - I certainly don’t trust this kind of “gamey” behavior and I definitely think he has ulterior motives. If it was me, I’d tell him I am not interested in maintaining a friendship with him and he needs to stop contacting me.