I think it's more about gender differences than self-confidence per se. Because the article could as well say, when a male scientist is talking to a female scientist, he tends to tune down his words and tries not to appear too agressive because he doesn't want to confirm the stereotype of "an alpha male" and offend the female conscientist. That's when I think he would actually appear less confident to an outsider. So confidence doesn't play a role in his mind set there.
But I understand your point. it can be transferred to stereotypes of different races and nationalities. We talk differently to people from different background. When I talk to an American, I am more concious of my accent. I sometimes hesitate when I use something I am not sure of. For example, I was talking to my manager, I used "she is trill" because I heard it before. So I checked with him right after the comment, saying, you say that? But when talking to a non-native speaker of English, I feel more confident about my accent and avoid using idioms or slang or words I am not sure of.
