Windows 10 PC with only a local account downloading One Drive Files

I was preparing an old desktop for sale so I did a clean reinstall of Windows 10. I removed my online Microsoft account and created a local "Newuser" account with its own PIN. When you look at settings/accounts it shows no accounts. Wiped the drive for security reasons.
Today I booted it to make sure everything is ok prior to sale. I noticed that there were now files in my documents and pictures from a laptop I gave to my daughter last week. Also there were files from a Civilization 2 game. Somehow it appears that One Drive is still sharing files between these PC's even though all accounts were removed from the old desktop? What a security nightmare! We just uninstalled One Drive from both of these computers and deleted all the files. Does anyone know how this can happen and if the old PC is still a security risk? Could the new owner reinstall One Drive and suddenly have access to her files?
Thanks

Yes, it was a clean install from a new download.

However, it forced a Microsoft login to proceed with the install which sucks.

Following installation I created a new local account and deleted my Microsoft account/login using settings/account.

I thought this was enough.

My daughter was using a laptop with my account. She never asked for anything to be uploaded to I Drive and I have never used it. Much to my surprise her data started showing up on the PC that I was selling even though the Microsoft account was deleted. Microsoft hypes security big time but leaves gaping holes when it come to their "preferred" apps.

Yes, I had done the clean install removing the partitions and installing on unallocated space.
The bad thing was that the install forced a Microsoft login to proceed. I thought I was safe creating a generic local account and then deleting my Microsoft account. Surprise! Fortunately I booted it one last time before giving it away. I had forgot about doing the install with the network disconnected to get around this fiasco. Just did it all again with the network unplugged. Thanks again for the help. Kind of amazing that even after this clean install with only a local account and the device not listed on my Microsoft devices page, it still says Windows is activated with a digital license!