Calling it art doesn't mean the same as calling it good, and calling it commercial doesn't equal calling it bad. Commercial work can be done quite artfully, or by an artist proper, and art work can be done quite commercially as well, if that is part of the concept.
However, calling something art based only on the medium has always been a weird and overly technical argument for me. Something's physical being does not define it. Its use does. These photographs were made, arguably using artistic techniques and concepts, to sell magazines, not to make art.
Your questioning the author's argument makes perfect sense if this were existent fine art work that was "[put into] Playboy". However, this a phrase with which I disagree. This is not something that was already in existence as "art" that was then selected for placement in the magazine. It is work that was made specifically for this purpose. Thus, "putting it in Playboy" is its entire purpose for existing in the first place...and it is thus commercial photography.
Now, Hustler...THAT is ART!