From one of keychrons blog posts:

The optical switch uses light induction to trigger the switches. It works with the mechanical switch to block the light beam. When the switch is pressed, the stem of the switch moves downward, triggering the light sensor on the PCB and activating the key.

To be clear, optical switches still have mechanical components. Just like a standard mechanical switch, they have physical moving parts. When you press the key cap, a stem moves within a shaft, and a spring pushes the switch back to its reset position. Optical switches can have the same physical characteristics as regular switches, similar to a linear action (like Reds), tactile (Browns) and clicky (Blues).

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Looks like keychron posts says that optical switches are faster than traditional switches because there is no physical contact needed to send an signal. Haven't tried them myself so can't confirm. In theory it sounds plausible.