From the article: "The authors are not talking about a political realignment. Democrats continue to overwhelmingly outnumber Republicans among faculty, young and old."

I think they are just describing the younger faculty being less activist about their political views. Take a look at the second graph they provide. There is a small increase in conservatives in the social sciences (probably due to increases in the percentage of economists), but little else to support the claim that faculties are becoming more diverse.

Even that, I'll be very skeptical of. At every university I've been to, self identified "liberals" are socialist and self identified "moderates" are merely left wing democrats.