Yes I get that Bridget. But to mistake him for two people? 
They didn't. They mistook him for a woman when they looked through the window and reported that. When they went in they found they had made a mistake and reported one dead male (can't recall whether the same officer made both reports but H will). Control misinterpreted that as two bodies, one female, one male. they never reported 3 further bodies upstairs, they reported 5 in total, and control did the maths based on their earlier misinterpretation.