I think this article chose CMU because for Computer Science and technical startups, it's well understood in the valley that CMU is a top 4 school (and for many, a top 2 school) for producing software engineers, which tend to underpin a lot of tech startups.
Totally agree if you move outside of software companies that this makes sense. Anecdotally, I'll say CMU tends to produce individuals who are technically overweight but perhaps lacking in business sense. This is both because of school culture and the broader Pittsburgh community.