Impedance mismatch between two pieces of equipment (amplifier and speaker, in this case) is a thing, and depending on how the amplifier is built can be a problem. But for the piece of wire connecting them to behave like a transmission line it needs to be a significant fraction of the wavelength of the signal, which at audio frequency is quite a lot, so unless you have your amplifier on the other side of town it is totally irrelevant. The guy was blabbing nonsense. We didn't talk about quarks.