I will certainly agree: there should be more skepticism for such at article by a known untrustworthy author. Does that mean we should immediately dismiss something written by him?

Your advice is good to take in general: don't trust what you read without judging both the credentials of the writer and the content the writer is putting forth. But to dismiss it based only on the author is shortsighted. I see nothing in your reply specifically about the content of the article, does anything else truly matter? Sure, take the author's history and intentions into consideration, but at the end of the day the content is what matters.