isn't debouncing used for buttons?
Correct, and that is what more or less is inside a rotary encoder.
But for a potentiometer filtering can also be useful, and that is what capacitors in combination with resistors do. Filter.
I will check your added pictures.
Edit1: Pin 1 of the potentiometer is connected to ground, and my guess is that the left and right inputs are connected to the pins 4 and 5. On the backside of the board it might be that the signals are lead to the other side with vias, but I'm not sure about that.
Edit2: After a better look it seems the signals are connected at the other side of the capacitors and come from the two transistors below near R157 and R172, and the capacitors are for decoupling to get rid of a DC component.