My smartphone is more powerful than PCs several years ago and only slightly larger than a standard computer mouse, with the majority of its internal volume being the battery, so I'm not surprised this could be done.
It's not like the idea of putting the majority of the computing power in one of the peripherals is new either - many early home computers like the C64 and ZX did this with the keyboard, and early game "consoles" appeared with most of their circuitry located in the controller.
It's not like the idea of putting the majority of the computing power in one of the peripherals is new either - many early home computers like the C64 and ZX did this with the keyboard, and early game "consoles" appeared with most of their circuitry located in the controller.