Threatening César would not stop him from telling her. You know it wouldn't. It's too late.

César keeps it at that for now. He's given Dabi the information he needs for the moment. The rest he can get later, likely a lot of it from Magne herself. And seeing her here will be worth more than a thousand words....

He speaks again and points at a building as they make the last turn. "I expect your shovel talk later. For now: that's the Oak & Iron."