The bass sounding muddy and the high notes sounding distorted has "poor encoder" written all over it.

Depends on your definitions of "muddy" and "distortion".

A low-quality encode would lose some detail and cause audible artifacts, yes. But genuine clipping distortion? No.

If you use the word "distortion" to describe encoder artifacts, I could understand. But to me, distortion means actual clipped waveforms, not a loss of high frequency detail. When someone tells me "distortion", I start looking for gain-related problems, not encoder problems. His description did not sound like poor encoding to me.

Now, a bad rip... I could see that being described as distortion, depending on what the ripping problem was. For instance, the analog-sample thing I described above could easily be distorted. But that's not the same as a low-quality encode.