I think the original author was referring to the wave of popularity a few years ago when Mongo / redis / cassandra/ etc were getting tons of press, "SQL is dead

I think the original author was referring to the wave of popularity a few years ago when Mongo / redis / cassandra/ etc were getting tons of press, "SQL is dead" was the going phrase, and document pre-joins and intense searching of object/documents via map-reduce (elastic, et al) was the metaphor du jour. Like every other hype, it settled down to a realistic set of use cases that NoSQL databases rock at, and the world recognized that other use cases weren't their thing, and you stopped hearing about the death of SQL, the expectation that you'd never need a SQL DB or join again, etc. So, not a fad, but past the hype-beyond-belief stage and now into the "gets stuff done" stage.