That doesn't make it ad hominem. That's a phrase used in the context of a debate. jessedhillon isn't after the argument at all. He's attacking a certain behaviour.
ad hominem: "Your point about global warming is invalid because you slap your children and I don't like that."
not ad hominem: "You slap your children and I don't like that."
He basically admits he didn't even consider the arguments. He calls the person a coward for posting anonymously. He's attacking the person's behavior irrelevant to the argument. Attacking the man, and admitting he never considered the argument at all. So if it's not considered ad hominem it's just trolling.
