I'm not a native English speaker, so I had to look it up, but I think I'm using the word correctly:

https://en.wiktionary.org/wiki/stereotype#English - A person who is regarded as embodying or conforming to a set image or type.

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.

that's actually exactly what stereotyping is. so if you agree with the statement in the article then you must agree with all the other stereotypes out there.