He also defines mad as "MAD, adj. Affected with a high degree of intellectual independence; not conforming to standards of thought, speech and action..."

You shouldn't take anything in that book too seriously, everything is tongue in cheek.

Bierce went to great length to be cynical and curmudgeonly in all his writing ( and a lot of his life) . If you look at the very rapid development of the technology of recording and reproduction, going from from wax cylinders to plastic disks, the great variety of recordings made, and even special versions of musical instruments ( like the Stroh violin) invented purely for recording, it's obvious that there was a lot of interest and a booming market, and Bierce's opinion was out on the fringe.