A dual-boot PC runs two operating systems on the same hardware, picked at startup. It raises an interesting question for hardware identity: are the two systems the same machine, or different ones? The answer is "both, depending on the identifier."
Identifiers that differ between the two
Some identifiers are created by the operating system, so each install gets its own. Install Windows twice — two partitions, two systems — and each generates its own machine GUID, its own product ID, its own set of Windows-assigned values. The volume serial of each install's partition is also separate, because they are different partitions. To anything reading these software-level identifiers, the two boots look like two different systems.
Identifiers that are shared
Other identifiers belong to the hardware, and the hardware is the same regardless of which OS you booted. The motherboard's SMBIOS UUID and BIOS serial are in firmware — one motherboard, one set of firmware identifiers, seen identically from either OS. The network adapters are the same physical cards, so the MAC addresses are the same from both boots. A storage drive's built-in firmware serial does not change with the OS either.
What an anti-cheat sees
This is the practical consequence. An anti-cheat reading firmware-level identifiers sees the same machine from either boot — the SMBIOS UUID does not care which Windows started. An anti-cheat reading software-level identifiers like the machine GUID sees two different values. So whether two dual-boot systems "look like the same PC" depends entirely on which identifiers the anti-cheat relies on — and the firmware layer, the one ordinary software cannot change, is shared.
The takeaway
On a dual-boot PC, the software-level identifiers — machine GUID, product ID, per-partition volume serials — are separate for each OS install, while the firmware identifiers and MAC addresses are shared, because they belong to hardware that does not change between boots. The two systems are different at the software layer and the same at the hardware layer. Which one matters depends on which layer is being read.