IMHO the main point of the French article is that the rotation speed of the galaxy decreases according to Kepler laws for the outer parts of our galaxy. They're us a graph for that. This contradicts previous observations. They ask why our galaxy should be special and they suggest that we (they) measured rotation speed of stars in the Milky Way while we measure rotation of gas in the other galaxies. I'm not sure why gas and stars would have different orbital speeds, but well, who am I to actually understand this matter.