There was no disk, only a slot for one.
The crime isn't booting off an unused disk, the crime is that the computer didn't have an SSD in its SSD slot when it was shipped when it was clearly built to have one.
Also, to find an unused disk, on Windows you have to go to Disk Manager. idk what you mean by "check the volumes". If the disk is unused and not-initialized, there won't be a drive letter for it and it won't be among the volumes.