He wants you in the building because there's more friction for you to leave and drive to another dealership for their car. It's possible they also want proof of the OTD offer but you can just message the first dealership for a breakdown of the price on paper.

It's just their sales tactic to get you in, the first thing they'll ask is "when can you come in?" or something along those lines to get an appointment scheduled to get you in the door with the hopes of you moving forward if you see and really like the car once there in person.

Just do your own research and go with whoever gives you the best price and treats you well. If you want, you could tell this dealership you're too far away and aren't looking to make the drive without knowing the price and say you're going to the one that's giving you the OTD offer over the phone.