While the article does offer some rebuttal to that claim, I'd like to give a stronger one*: California is 31% white, University of California students are 25% white - they are underrepresented.
https://en.wikipedia.org/wiki/University_of_California#Stude...
*Edit: On second thought, grardb is correct: Comparing with K-12 demographics, as the article does, is better.