The signal is recorded and played back. The actual electrical signal can be positive, or it can be negative. When the recording is being stitched together, the mixing devices can sometimes allow parts of the signal that were positive to be reversed and be negative, or the whole thing negative.
Part of this is every 'electronic stage' reverses the signal. Most devices have stages paired, but sometimes the device can use one stage, and the signal winds up reversed.
So when this hits your speaker, the reverse signal actually DOES make the cone go backwards from what the positive signal would do.
This reverse signal makes music just as well as normal, except the waveform is reversed. And a few folks can hear this easily. Some can hear it sometimes or a little, and many cannot hear it at all.
If you have a speaker cone off the cabinet, and touch a battery to the leads. the cone will move one way. If you reverse the leads, it will move the opposite direction. Same thing with inverted polarity on music
So for some folks, this is a big deal, because they can hear it all the time. For a few folks, who can hear it sometimes, it usually does not matter too much. And for the majority of folks, either because they do not know what to listen for, or because thier ears just do not catch the subtlties of it, and some claim it really does not matter at all, and could care less.