It's comparing the same title (roughly, with some errors, but that's expected I think), and returning many editions. Some of those editions might be trade paper

It's comparing the same title (roughly, with some errors, but that's expected I think), and returning many editions. Some of those editions might be trade paperbacks, some might be mass-market on newsprint, depending on the book. (One book I searched returned among other things an audiobook on cassette.)