That is interesting, I would think that if you remove the params from the single page app, publish and save that so that the params no longer appear, then go in import it to a multipage app they should not be 'following' into the multipage app
You may need to delete that page from the multipage app and try 'creating' the page natively inside the multipage app with some copy/pasting of components and queries over if the ghost params are still there after deleting the imported page
Just wanted to check back and see if you had figured this out. It may well be a bug in the importing process where if a single page app has params that they are then 'baked' into the multipage app.
If you are still having this issue, let me know and if you give me the steps to reproduce I can file a bug report to our multipage app team
I just went to test out the URL params and can confirm that we have depreciated single page apps. All new apps are now multipage by default and thus have their URL params configured on a single settings input that is responsive to changes.