The CEO of a company that promotes hackathons wants to try to convince the world that all forms of recruiting are old-timey except for hackathons.
Take it with a grain of salt.
I don't see this article actually supporting the assertion that career fairs are declining. In the technical majors at my school (UMass Amherst class of '14), they were the first steps to getting internships and jobs for almost everyone who got them. Nearly every CS junior and senior, and many-to-most sophomores, went at least once, if not twice, per year.
This is my experience as a current student at an predominately engineering/technology university. Our career fairs are very large and almost all junior/seniors attend. Its been growing steadily every year as well. That's not to say that companies don't try to get a head start (for example, tons of companies are having lawn events and other informationals, which really just mean they want resumes from interested students, for a few weeks before the actual career fair), but the career fair is definitely the central employer-student communication venue.
Since when did they ever? Was this really a thing? It seems to have come and gone without affecting me or anyone I know.
They are very common at universities which, I think, was the focus of this article.