The small student population at Olin affects the founder rate in a more pertinent way than sample variance: because they only need to admit 100 students, this group of students can be of a higher average quality than if they needed to accept 1000+ students like Stanford/MIT. As an analogy, if YC were to 10x the number of startups they invested in per batch, they'd certainly expect their average return to decrease, because the last company they accept will be less likely to succeed than the first or tenth.
If you really wanted to measure how Olin's teaching compares to that of MIT/Stanford, vis-a-vis startup founding success, you could have the other schools "draft" a team of 100 CS students at the beginning of their freshman year, and measure the founding success rate of only those 100 students.
That is implicit in the studies done in the paper, in that Cooper Union, Harvey Mudd, etc don't figure in the top universities that follow after Olin on these metrics.
If you really wanted to measure how Olin's teaching compares to that of MIT/Stanford, vis-a-vis startup founding success, you could have the other schools "draft" a team of 100 CS students at the beginning of their freshman year, and measure the founding success rate of only those 100 students.