Wasn't there a topic about a very similar concept (although it was about checks, not checkmates) a few weeks ago? Anyway, yes it is checkmate. To give a rather crude interpretation of the rules, you can say that whoever can "capture the opponent's king" first is considered the winner. So, if white king takes the queen then the black rook "takes the king" before the black king can be captured, so black wins this game.
A little less crudely, it can be said that the concept of "check" is not affected by whether the piece delivering check is pinned against the opponent's king.
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