That is a completely different statement than showing that it doesn't matter what school you went to. Your article appears to me like it is conflating the two.

(1) Conditional on having applied to YC, YC finds that having attended a prestigious college makes one no more likely to be selected for interviews.

(2) Conditional on having been selected for YC interviews, YC finds that having attended a prestigious college makes one no more likely to receive YC support.

(3) Conditional on receiving YC support, YC finds that having attended a prestigious college makes one no more likely to succeed in the market (here defined as visibly thriving within about a year).

Given the initial essay's strong emphasis on market success as the ultimate verifier (paragraphs 5-8), I thought the main idea was (3) -- but if interview invites/subjective-evaluations are a factor, some amount of (1) and (2) are mixed in, too.