Could it be that the exit rows were originally held, but these people upgraded?
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Way out possibly, but if that was the fact there was only about 4 revenue / upgrage pax judging by the unused seats on landing.
Way back as above the seats were available on the seat map but returned an error when trying to purchase. The phone agent advised they were occupied despite that, and on the evidence of them being empty I would suggest that the seat map was correct!