I suspect it's more bland than that, they need to be able to have a booting/working system otherwise the customer is going to call up support and say their computer isn't booting or that it's saying "no OS found" type messages. It's just to cover themselves, that's why they include enough Linux to be able to load a PDF reader. It should be easy enough to do d:\setup.exe with a USB that has a Windows installer on it, with this setup.
Windows installers are bootable these days (from DVD or USB; doesn’t matter); they haven’t been runnable from DOS for a couple decades now.
At any rate, even if you did find some OS you could install from DOS, you’d be installing it into the QEMU image if you installed from FreeDOS on a system with this arrangement. There’s no way to get back to the bare metal hardware from FreeDOS here.
It's probably more like they have DOS support contracted out to some vendor. And when the systems upgraded to the point of not being able to run DOS natively the vendor built this franken-OS to fulfill the contract.
Renegotiating the contract to something sensible like "don't run DOS anymore" was probably hopeless in the face of the bureaucracy, or risked losing to contact.
