Read the article again. The Economist controlled for a variety of factors. Family socioeconomic status was among them.
That said, one of the shortcomings of their metric is that they only had data on students who took out federal loans. How predictive this result is for others is open to question.
Well, then, it's even more glaringly bad-form to leave out two-year and vocational schools from their approach then, if socioeconomic status is a factor, now isn't it? My perspective is yes, it's bad. It seems we'll just keep talking around each other, but I'll stand by my thumbs up toward the Brookings version and give the hairy eye to The Economist's method.
