PCM doesn't make any special case for different wavelengths. It's simply the air pressure over time (pressure on your ears, on the speaker's membrane, etc.) It doesn't directly correspond to the volume ("f(t)=1" is as silent at "f(t)=0").

So yes, an (uncompressed) audio stream is just a sequence of samples of pressure (or displacement, depending on the medium).

The variety you get comes from the high sampling frequency: a high sampling frequency allows representing vibrations of the air pressure at many frequencies.