Does the author actually define "metagame" anywhere? He seems to use the term throughout the article to mean multiple subtly different things.
If there's a really popular rush deck, do you drop some cards which shut down blue control and put in some anti rush cards? That will help when you match against the rush deck, but if everyone does it, then when you reach the finals you might be against the control deck.
That's the metagame, at least how it's used in those circles.