Every USB device that connects to your PC introduces itself — and that introduction carries information that can contribute to identifying your machine.
What a USB device tells the system
When a USB device is plugged in, it reports a set of descriptors so the operating system knows what it is and how to use it. These include a vendor identifier, a product identifier, the device class, and often a serial number. Your keyboard, mouse, headset, webcam, controller and storage devices all do this. None of it is hidden — it is how USB works — but together it is descriptive.
How it becomes a fingerprint
A single common device is not identifying. The signal is in the combination. The particular set of devices connected to your PC, and especially any that report a unique serial number, forms a profile. Two PCs with the same model of mouse look alike on that point; a PC with a specific external drive that has a unique serial is more distinguishable. As with browser fingerprinting, the principle is that a combination of ordinary traits can be uncommon enough to single a machine out.
Stable versus changing parts
Not all of it is stable. Devices you unplug and move around — a flash drive, a headset shared between PCs — change the picture. But devices that stay connected, and especially built-in or permanently attached USB hardware with fixed serial numbers, are a steadier part of the signal. Software that fingerprints a machine weighs the stable parts more heavily than the parts that come and go.
Where it fits in the bigger picture
USB device data is one input among many. Anti-cheat and device-identification systems combine it with disk, network, registry and firmware identifiers. On its own it is a weak signal; alongside the others it adds detail. It is also a reminder that "hardware identity" is not just the core components — the peripherals attached to a machine describe it too.
The takeaway
USB devices report vendor, product and often serial information as a normal part of working, and the set of devices connected to a PC — particularly any with unique serials — can act as one fingerprinting signal among many. The stable, permanently attached devices count for more than the ones you move around. It is a small piece of the larger hardware-identity picture, not the whole of it.