Why were some of my folders moved into the Dropbox folder, leaving behind aliases, on Mac OS Sonoma?

     Last night I experienced a weird and unsettling problem. All of a sudden, without any discernible reason, I lost permissions to access both my Desktop and Documents folders in MacOS Sonoma 14.6. Running Disk Utility and CleanMyMac to try to fix the problem did not work. I wound up calling Apple Support and got the problem diagnosed and solved, but I want to know how it happened in the first place.

     Here's what the situation turned out to be: both my Desktop and Documents folders had somehow gotten migrated to my Dropbox account (inside of a folder named Mac) and in the process I lost access to them. Apparently what I'd been seeing in my Desktop and Documents folders were aliases pointing to the Dropbox location of the original files. How did this happen? I certainly didn't put them there myself. The files are still there, because I'm kind of afraid to move them back to their original home, lest I lose them altogether in the process.

   So, I need to know if it's safe to move them. Unless there is some good reason (i.e., a good feature in Dropbox) to keep those files there, I'd really like to move them to their proper home on my hard drive.

   I'd really appreciate any help and guidance I can get on this. Thanks ever so much!