While I generally agree with that, that’s not what seems to be happening here. What seems to be happening is that anyone who boots Windows via grub is getting grub itself overwritten.

When you install Linux, boot loaders like grub generally are smart and try to be helpful by scanning all available OSes and provide a boot menu entry for those. This is generally to help new users who install a dual-boot system and help them not think that “Linux erased Windows” when they see the new grub boot loader.

When you boot Windows from grub, Windows treats the drive with grub (where it booted from) as the boot drive. But if you tell your BIOS to boot the Windows drive, then grub won’t be invoked and Windows will boot seeing it’s own drive as the boot drive.

This is mostly an assumption as this hasn’t happened to me and details are still a bit scarce.