Even when just looking at the title, it's safe to assume that CMU is some kind of place, more specifically, an organization and/or institution. Reading the first sentence of the article -- "I'm leaving CMU to join Amazon" -- brings even more clarity, that "Leaving CMU" refers to a changing of occupation. The next sentence talks about machine learning, so it's safe to say that the author is in the AI/machine learning space, and that CMU is a place that, like Amazon, has some expertise in it.

At that point, if you haven't already guessed that CMU means "Carnegie Mellon University" -- an acronym that's not quite "MIT" but still well-known in engineering circles -- you'll get the definition in the very first Google search result, even for just "CMU"