An ad hominem isn't just any time you say something mean about someone. An ad hominem is when you say that some thing someone believes is wrong on the basis of some irrelevant personal characteristic. ("John may tell you that the Higgs-Boson exists but he is a convicted felon!")
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.
True, but a common argument against stallman's arguments is often "I don't want to listen to some smelly hippy with a greasy beard" rather than debating his points directly.
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).