Maybe the intended audience for this article is the Times' own editorial staff? Or people who read Times articles like
this one unironically? They would undoubtedly be relieved to learn that they have never been Sanders' target demographic.
Universities aside, there's not much reason to conflate "affluent, secular, [and] well-educated" with "liberal activist" or "left-wing." In any case, there are good reasons to look at attempts to measure ideology with skepticism; most voters aren't self-aware enough to know how to classify themselves and have well-developed opinions on only a few issues at most. It's extremely difficult to design survey instruments that work around these tendency.
The more useful headline is that Sanders will probably have weak support among older voters, women, and minorities. Will he do as poorly among white non-professionals as this piece implies? That's more difficult to say. Some political journalists equate Sanders with the brand of anti-war liberalism that was dominant during the Iraq War, but Sanders is
not Howard Dean, Dennis Kucinich, or, God forbid, Mike Gravel, and we're living in a political landscape in which other issues - the economy, corruption, etc. - have become far more salient than foreign policy to most voters.