Earlier quoted context omitted.
The other possibility is that going to the parties is a good use of time, and that is where many students develop their networks. In addition to that, signalling theory would indicate that what classes you take and how well you do are much less important than the university you attend and the faculty you graduate from.
Would you say that going to parties outweigh directly networking? Networking might be a benefit, but I'm sure that people go to parties with a different goal in mind, and that the time cost of partying can be better utilized in other ways.
However, I can confidently say there's a big difference in the bond formed between two people chugging beer bongs together vs asking someone in a lecture if they'd like to have lunch.
I also think the party scene would be difficult to replicate in terms of the sheer size of your potential network (I make no assertation about the objective quality of that network, but the article suggests it's not what be predisposed to think).
Anecdotally, I've got lifelong friends from both camps; but the people I lean on now in my professional development are the people I partied (hard) with at university.