It is not an ad hominem attack to suggest that someone doesn't understand the subject matter. An ad hominem argument is an attempt to win an argument by making

It is not an ad hominem attack to suggest that someone doesn't understand the subject matter. An ad hominem argument is an attempt to win an argument by making claims about the person's character that are irrelevant to the argument. Saying, "I don't think this person understands what he is talking about," is not an ad hominem attack, because it is relevant to the argument. It might be unjustified, but that's another matter entirely. Apparently, since I just looked this up, calling someone a moron isn't an ad hominem attack either, but merely verbal abuse, so I retract my earlier statement where I accused the author of an ad hominem attack. As to whether the author has a point, he might do, but unless he puts forward a good argument we can only wonder.