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I believe it's a reference to Samuel Johnson's quote: "When a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully."

Interesting, hadn't heard about this.

I've definitely heard the phrase "concentrates the mind" when describing something so concerning that it takes away attention from other things to be dealt with. It's quite uncommon, though.

"Mind-concentrating" makes sense as an adverbial formulation of that phrase.

Just The Economist being a little playful with language. It primes the reader with the connotations of phrases such as 'mind-blowing' but then steps away and uses under-statement. The result is a mildly humorous collision in the reader's mind.

Mind-blowing. Mind-boggling.

These are the only two I think I am familiar with, never heard 'mind-concentrating' before nor does it make much sense.