Friend's OneDrive for Business appearing on my Mac Word
Solution 1:
Thanks to Microsoft support, it appears that the answer can be found here: How to remove Office license files on a Mac, using the License Removal Tool.
After running it, the access to the OneDrive for Business went away, and I just needed to do a simple re-log-in on my personal account to be back up-to-speed. 👍🏻