This may be sarcastic, it may not portray RMS in a good light (I disagree: I think everyone knows RMS is principled to the point of pig-headed; it doesn't change my opinion of RMS at all, just simply confirms what I already know). But it isn't an ad hominem.
People claim things are ad hominem falsely so often that some people have even started referring to it as The 'Ad Hominem Fallacy' Fallacy. http://plover.net/~bonds/adhominem.html ;-)
I'm not sure if that is the case with this article, but it does put a lot of text into describing his appearance rather than discussing what the implications might have been if the hackday had been focused around free software music projects (stuff like LMMS , ardour etc).