The pair of parallel conductors (wet string) forms a balanced transmission line[1] just like the copper pair in traditional phone line. The ADSL transceivers at each end automatically adapt to the available transmission line; you'll note that instrument reports that this 2 meter line looks like 4.5km of copper; it is a very poor conductor, so the ADSL transceivers fall back to lower frequency operation, which is apparently sufficient for low speed communication.
I do wonder about impedance matching here. Traditional phone lines apparently have a characteristic impedance of either 600 or 900 ohms. That pair of wet strings look to be separated by about the right distance to produce impedance in that neighborhood, or maybe the line length is tuned to eliminate reactance. It isn't mentioned but I suspect that RevK understood this.