This article just skims the surface of the question it raises. For one thing, it doesn’t talk about alternative sources of revenue (endowment, gifts, patents and contracts, tax-based support from state and local governments, etc.).
Second, it doesn’t talk about costs and expenses to the institution to provide education (teaching and advising, general management and planning), housing, and services (extracurricular programs, recreation, health and safety, etc.), facilities maintenance (buildings, labs, landscaping, etc.).
Third, it doesn’t touch on the market – competition – as a factor in the nominal and actual cost per student-year.
Fourth, and this is a more general issue that’s related to the the first two, it doesn’t talk about management efficiency and efficacy – something that has been subject to a lot of discussion in recent years owing to the bloated administrative hierarchy (provosts, deans, subdeans, chairs; special offices for every kind of service including intellectual property, occupational safety, financial aid, inclusion, etc.).
Fifth, it doesn’t talk about the general inflation in the cost of everything. While the net cost of college education has certainly accelerated faster than general inflation, it’s important to realize that the latter is nonetheless a factor. Since the year my kids were both in college in 1999 (they overlapped 1 year), the general cost of living has risen 42%. That should be taken as a baseline expectation for the increase in costs of college education between 1999 and 2015 (based on BLS cost of living calculator).