This exact point is where the note's information falls apart.

The note says it's a gain control. Gain is the amount of power increase when a signal is amplified. So... that control actually modifies the gain of a stage? Nope. At the very least, the best way to change the gain is to adjust the negative feedback of the amp, and any noise introduced by the control would be massively amplified. Bad, bad idea.

EVERY volume control on every A/V receiver, for instance, is not a gain control; it's a signal attenuator. Going to the watering system metaphor, a gain control is a pump pressure adjustment while a volume control is a faucet. The fact that we think of "turning up the audio" and "turning off the water" are opposite concepts doesn't mean they do anything different from one another.

If the input to the Snap amp is an opamp and too hot of a signal cannot be brought down below the level at which the opamp will distort, then Snap has created the problem. If the input is some passive circuit followed by an attenuator, then they can cut down the too strong 2 volts to a value that won't cause the following stage(s) to distort.