I’m not sure I fully understand, how has your fresh install already got the same users?

Simple Press is tied to WordPress, so uses WordPress users and other data. Normally for example when talking about moving to a new domain, you would move the whole install including WordPress, not just the forum.

You can move select parts of a database to another by exporting the tables that start with sf, for example if you’re using the standard wp prefix you would be looking to move anything that starts wp_sfxxxxxx.

One problem though, if your new users id’s don’t match the ones from the old database then nothing will match up properly..