This definitely isn't an ad hominem, and it isn't even analogous to one. Enraged_camel is implying that libertarianism is missing something that is easy to miss if you have led a relatively comfortable and unchallenging life. The criticism is oblique rather than explicit, but that doesn't make it anything like an ad hominem, because ad hominems are essentially distracting with irrelevancy.
They make for witty-sounding quips, but both are ad-hominems[0] that do little to actually address and argue against the tenets of either philosophy.
[0] (In before someone points out that this is not a true ad-hominem because it attacks a stereotype (and a straw man at that) rather than a specific individual).