And if you look at the rest of the data (i.e. the "National Center for Education" "Digest of Education Statistics" "Table 322.30")
You will notice, that if you breakdown the ethnicity into percentages of degrees conferred, for "computer and information sciences" for 2011-2012, you will see there were 47,384 Bachelor degrees earned by students, of which 30,211 identified as "white" (63.75%), 5,410 as "black" (11.41%), 4,008 as "hispanic" (8.45%), and 4,254 as "asian" (8.97%). There are also another 2,360 "non-resident alien" listed which no ethnicity is given.
Now looking at people working at Yahoo!, 50% White (13% less than percentage earning degrees in USA in 2011-2012), 39% "asian" (30% more than percentage earning degrees), 4% hispanic (4-5% less than percentage earning degrees), 2% black (9% less than those earning degrees).
If you look at all the other companies on that list linked in the article, you will see roughly the same trend, with "whites" having about the same proportional makeup of the companies as there are those getting degrees, asians having a much higher percentage of the workforce than are getting degrees in the US (wow, not surprising since we are importing most of this labor via H1B, green card, immigration), and blacks and hispanics having slightly lower than the amount they graduate.
Now the lower amounts of blacks and hispanics may very well be simply due to location. The companies they looked at are Silicon Valley companies, with the majority of their workforce in California. California has a much lower percentage of blacks than say Georgia, Mississippi, Alabama, etc... If you even slightly believe that the percentage of graduates are equally spread out across the nation's schools based on percentage of population in the schools, and that attendance in schools more closely mimics the population in the state (not always, there are historically african american shools as well women only or male only schools, and schools certain ethnicities would never even want to go to for many reasons), and take into consideration that most people will tend to stay close to home/family when searching for a job, and you will see that the breakdown of ethnicity in Silicon Valley tech companies is probably really not that out of step with the percentage of population in the labor market in Silicon Valley.