Supposedly the podcast is a guy doing a Boston sports radio show, which would explain how he had Casey on. But who knows. He could've simply said Ben wasn't doing The Batman, as in not directing it, and it got taken as not acting in it either. Or maybe he said he's done playing Batman, and it turns out to be the case, then it is what it is.
This whole discussion of Ben leaving happened not too long ago. Haven't changed my thoughts on it. If he doesn't want to do it anymore, let it be. If he continues, that's cool too.
What's interesting is the idea tossed around about Reeves' Batman trilogy being standalone. If so, who knows. Affleck sticks around as DCEU Batman, appearing in team ups and such. Another actor is in the solo trilogy. It's what WB wanted to do nearly a decade ago.
edit: Casey's exact quote is,
"He's not gonna do that movie, I don't think."
then he jokes about playing Swamp Thing
I misheard but he supposedly also says "I was just kind of making that up" after.