Their listings include colleges with 5 year graduation rates >= 75%, a proxy for high selectivity (179 colleges out of about 3,000 total four year colleges in the US). Six of the nine UCs made that threshold (UCSC, UCR, and UCM were the ones that did not).
See the top paragraph of http://www.nytimes.com/interactive/2015/09/17/upshot/top-colleges-doing-the-most-for-low-income-students.html .