That doesn't make any sense. If you installed Linux first, there would be no Windows partition for GRUB to autodetect when it was set up. And GRUB doesn't probe for operating systems automatically on boot, only when you run "update-grub" from inside a running Linux OS, so it wouldn't magically fix itself once you did install Windows. And besides, the fact that we are talking about GRUB autodetecting things, not Windows Boot Loader, only proves the parent's point.

A kernel update reruns grub config which then adds windows to grub