The question then is: is your site already populated? or is it just a newly installed WordPress?
If it’s the second, then the simplest thing to do is just go change the hosting back to the desired user and reinstall WordPress.
If you’ve spent a lot of time populating data, you could re-install WordPress using the same database, and then re-appply your theme and you should be back to normal.
Or if this is a heavily populated large existing blog, you could copy the files between the users a few ways, one is rsynch with the remote being the other user on the same machine.
Also, when you switch the user by editing the domain from “Manage Domains” in the Dreamhost panel it might give you the option to “move” the files to the destination user. I’m not sure if that option is present when the other user already exists, to be honest I’ve not tried doing it that way. I do know that if you change and are creating a new user at the same time it will give you the option to “move” the files to the destination user.
And unless they changed the language in the panel since i’ve seen the message it does use the word “move”, however it really means “copy”. The difference is after a successful “move” original file is deleted. Since a copy of the files is left behind this operation should really be called “copy”, not “move”.
Caveat: things can go wrong with copying between users, the most common thing being the username hard coded in a path in some file that was auto-generated. It’s not supposed to happen that way and WordPress core won’t do that. A plugin or theme might do some thing silly like that, although they shouldn’t do it that way.