This iCloud backup includes purchases from the iTunes Store that were made with a different Apple ID

I backed up my wife's old iPhone 6 to her iCloud account, and ordered her a refurbished iPhone 10 from apple.com. Today we got her iPhone 10 in the mail. I powered off her iPhone 6, swapped the sim card over to the iPhone 10, powered it on, and followed the set up instructions. I choose the option to restore from an iCloud backup, and selected the backup that I created yesterday. After some various screens, we received the message:

"This iCloud backup includes purchases from the iTunes Store that were made with a different Apple ID. Enter the Apple ID password for "staceyhawking@yahoo.com" to restore these purchases."

That is not my wife's name, we have no idea who that is, and we do not recognize that email address at all.

At this point my wife and I were concerned that someone possibly compromised her account and somehow ordered things from the credit card associated with her apple ID and somehow used it on their Apple ID. I called Apple support, and the younger guy said he had no idea what it could be. I suggested that maybe it was residual data form the last user from the phone being refurbished, and he said yes, that was it. He wasn't very confident in his answer, hence me posting here.

I still thought it was very weird, so I did a full reset, with "Erase All Content and Settings", and repeated the process from scratch. Again I received the same message, so it appears that the data is included in our backup. We went through our entire 6 years of purchases associated with my wife's Apple ID, and it was nothing but $0 charges for free apps that she recognized, and $0.99 cent charges for our 50GB of iCloud Storage.

At this point, on that screen with the unknown address, I choose the "skip this step" and continued the set up process. When finally getting to the home screen showing all of her apps, another message popped up "Sign in to iTunes Store. Enter the password for your Apple ID "staceyhawking@yahoo.com".

I am afraid we will run into problems further down the road, and I find it hard to believe that Apple wouldn't completely wipe a refurbished device, leaking someone else's Apple ID to us.

Anyone have any idea what is going on, or where this unknown Apple ID is getting pulled from?