From what I have read it is only tied to the motherboard as others have pointed out.
But to be clear the support conversation appears to be related to the free upgrade process. Sounds like the guy completed the free upgrade, swapped hardware out, and now he can't reinstall Windows 10. Right or wrong, I can actually see Microsoft doing this. The free upgrade is just that, an upgrade. It is intended to install only as an upgrade on a system currently running an earlier version of Windows. If a hard drive was replaced and you needed to install Windows 10, you would have to either (a) install the full version - which would require a purchase; or (b) install an earlier version and go through the upgrade process again. The problem there is that Microsoft may only allow one upgrade per license key, in which case your previous upgrade voided that license key for future upgrades.
It would be similar to having Windows XP running on your system and wanting to upgrade to Windows 7. You go out purchase the upgrade license (cheaper) so you can perform the upgrade. A few months later your hard drive crashes, you try to install from the upgrade license and are out of luck. You need to go through the upgrade process again or have a full version available.
But to be clear the support conversation appears to be related to the free upgrade process. Sounds like the guy completed the free upgrade, swapped hardware out, and now he can't reinstall Windows 10. Right or wrong, I can actually see Microsoft doing this. The free upgrade is just that, an upgrade. It is intended to install only as an upgrade on a system currently running an earlier version of Windows. If a hard drive was replaced and you needed to install Windows 10, you would have to either (a) install the full version - which would require a purchase; or (b) install an earlier version and go through the upgrade process again. The problem there is that Microsoft may only allow one upgrade per license key, in which case your previous upgrade voided that license key for future upgrades.
It would be similar to having Windows XP running on your system and wanting to upgrade to Windows 7. You go out purchase the upgrade license (cheaper) so you can perform the upgrade. A few months later your hard drive crashes, you try to install from the upgrade license and are out of luck. You need to go through the upgrade process again or have a full version available.