I think that video is in error. It's correct when it says two types. One with signal line and a ground ( shield) connection. The other with two signal wires with inverted signal on the second wire.
Technically they are called Unbalanced cable and Balanced cable.
The Balanced cable does have two signal lines but ( at least in pro-audio) has a shield also, like the unbalanced cable. So it will have three separate connections ( and a casing) and uses an XLR plug . The first type uses an RCA plug , one pin and a grounded casing.
You cannot use an RCA connector to get the benefit of noise rejection. The XLR connector has no signal on the shield connection which the unbalanced line has.
In the video he shows the two plugs to be the same. However they do not work the same and the second one should really be a 3 terminal connector. As shown it's an XLR connection without a shield and the outside of the RCA body should not be connected to ground at the input of the amplifier !
The question arises if one can use the twisted wire ( unbalanced signal ) without a shield on a regular RCA connector. Well, the effect of a shield will be missing and possibility of EMI and hum pickup will be there. With very high impedance amps like say a tube amp , this is going to be very poor. You will get a lot of hum. However with a low and very low impedance systems like say 5K or 10 K ( or lower ) impedances and line level inputs ( typically 1 to 2 volts for full output ) you can get away with minimal hum at normal listening distances.
Why would one do this ? There could be many reasons but a simple one is that, a) you want to eliminate another dielectric on the cable and B) you want to use some special cable like say teflon coated single strand silver coated copper wire ( typically 26 or 28 swg) for the signal and return line!
I have actually tried this with a small twist to it. I used a third wire twisted along with the other two. The third wire is connected only at one end to the ground connection. The original signal is the usual unbalanced type using RCA connectors. The third wire ( connected only at one end ) is an experiment for producing a ground line (0 Volt potential, with no signal current on it ) near the signal lines. It sounds very good and has very little hum at normal listening levels or even at low volume. You will need to keep it clear off power cables and transformers and other noisy parts. It HAS technically and measurably far more hum than any shielded cable. But it does sound very good.
