Factory reset fails with Linux/Win10 dual boot

XPS 13 (9370) with Factory installed Windows 10 Home

I repartitioned, turned off bitlocker and secure boot and installed Debian using EFI boot. (I did not delete any existing partitions but asked Windows to shrink the largest partition and used the resulting space.) I needed to send my laptop in for repair and was reluctant to provide a user login as requested in the instructions. I backed up everything and performed a factory reset to take the laptop back to 'as delivered from factory' SSD contents. The results were:

1. Win10 no longer boots with a missing boot device or something similar message.
2. Linux (surprisingly to me) can still boot and run normally.

I'm not sure if this is the correct place to post this as the laptop was not originally a developer edition. But there is likely more Linux knowledge here than any other fora at Dell. I'm also not sure if this is expected behavior. It surely falls outside the realm of what is tested. 

I'm also not sure if this is an issue that Dell would be concerned enough to fix, but at least I can mention it here for any interested.

My expectation is that the 'factory reset' would check for the recovery partition and if found, replace all other partitions, including any new ones that were created. Clearly that's not what happened.

For any curious, I overwrote the entire SSD with the 'contents' of /dev/urandom and installed from media downloaded from MSFT. (I looked for but could not find a downloadable image for the Dell drop with all of the Dell stuff slipstreamed.)