If the minimum average IQ for a major is X, then there will be many students in that major with IQs less than X.

Also, keep in mind that the study is deriving IQ from students' performance on standardized tests. These tests are primarily intended to measure education, rather than intelligence, and so this might simply be showing that the average education level of college students is higher than the average of the general population.

If they wanted to be honest about the reliability of their data, they would have left the IQ column off completely.