Sweeping Frequency Capacitive Sensing?

Other Hardware Sensors
1

So I read this amazing instructable: http://www.instructables.com/id/Touche-for-Arduino-Advanced-touch-sensing/?ALLSTEPS

Apparently, this works by using "Sweeping Frequency Capacitive Sensing". What exactly is this SFCS and how does it work? Is its mechanism anything like RCtime? (where we measure an object's capacitance or resistance by charging/discharging an RC circuit and measuring the time it takes)

2

I went through the Arduino code and apparently it uses PWM to produce a range of frequecies one after the other (I guess this is where the "Sweeping Frequency" comes from.) Can anyone please explain the circuit to me? This looks a little like an LC filter, but what exactly is it doing here?