An ad hominem (Latin for "to the man" or "to the person"[1]), short for argumentum ad hominem, means responding to arguments by attacking a person's character, rather than to the content of their arguments. When used inappropriately, it is a fallacy in which a claim or argument is dismissed on the basis of some irrelevant fact or supposition about the author or the person being criticized.[2]
I think I understand it quite well. Read his response to Patrick's factual information. He dismissed it without providing any counter argument at all. He only criticized the person making the statement.
It doesn't get any clearer than that.