I would delete it after trying to determine if the reviewer was objective and fair. There is a constructive way to comment but this one appears to be destructive. I had one once and left it stand for awhile before finally deleting because it was not representative of the others I received.
I think in this case it was trolling. No indication of anything in there that they'd read the book, not even taking the time to spell out words ... it's a moment's negative immature impulse. Definite troll in my opinion. Pay no mind.
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Art