Which requires there to be some set image or type for the person to match. It would be stereotyping if the article was implying that white men are usually mansplaining skeptics or something of that nature. But merely stating the fact that this particularly group was actually all white men isn't stereotyping.
https://en.wiktionary.org/wiki/stereotype#English - A person who is regarded as embodying or conforming to a set image or type.