Did you have a separate ESP (EFI System Partition) for EnOS or you shared one with Windows?
It seems unlikely that a Windows upgrade would wipe another partition on the disk but it is probable that it would wipe the bootloader of another distro in case of shared ESP.
There was this recent case of EnOS bootloader being deleted by a BIOS upgrade for example:
Also, could it be the case that it has only changed the boot priority in the firmware settings?
Have you already checked it in the BIOS/UEFI settings?