To say, “it is absolutely selection bias,” infers the professors and curriculum of the school had no effect on the ability of students to become successful, venture-backed entrepreneurs. Which you cannot conclude given the data.
What you have experienced is confirmation-bias. Whereby, you have interpreted evidence to reaffirm your own beliefs. In this case, your belief is, “Olin College cannot be better than MIT, Harvard, Stanford, Yale, and the like because those schools are the best.”
When you allow yourself to succumb to confirmation bias, you close yourself off to the possibility there is a school which prepares students for an entrepreneurial life. Please do not close others off to the same possibility.