Wrong. Last time I installed Manjaro on its own SSD, then after installation was complete, I added another SSD to the machine, and installed Windows 10 on it, After reboot, There was no GRUB anymore, Windows used the boot partition from another SSD and overwrote it. It didn’t ask to use that partition, it just used it as if it was its own during the installation process. This is why I ALWAYS leave ONLY the Windows SSD I want to install Windows on, in the machine.
I also have seen on Windows 10 an update overwriting the boot partition somehow (update + automatic repair on reboot, or something like that?).
So definitely Windows does touch the boot partition from other OS without any reason.
And this is all on UEFI system.