Looks like it's not accurate by under repporting not over reporting. So their down time was likely worse!
I am making an assumption that if Microsoft saw a lot of false positive outages they would fix that, but might drag their feet if there was an outage that didn't get properly recorded (assuming it's automatic to begin with, it might be that a human needs remember to update it).
See, I can just as easily make up a story that explains the chart.