Not after a full breakdown of how this specific light dimmer works, but rather how a device in series can control a load.
A light dimmer has the following wiring diagram. As you can see, the light dimmer is in series with the load.
From my research, most household dimmers modify the AC waveform to reduce the RMS voltage, hence lower the light, rather than using a rheostat.
Most of the information suggests the switching is done by a TRIAC, but in here there seems to be a power MOSFET (IRF840A) with a heatsink. There seems to be a 555 timer and a 324 op amp, which I'm guessing does the modulating.
Of course a definite answer of how this device works cannot be observed without reverse engineering it, however in general I don't understand how a device in series can operate when it's purpose is to control the load. The circuitry needs current to operate, but it's purpose is to (partially) kill the power to the load, and thereby killing it's own power (since the device is in series).
This is my interpretation of how a device could modulate it, but it doesn't make much sense to me.