Why are people so bizarrely defensive about this?

This isn’t sensationalism. It’s a scientific study of actual real-world fuel use based on data from thousands of vehicles (at least ten thousand, I assume, based on earlier studies). If, as the study author says, internal combustion engines are being used more frequently than estimated, should it not be addressed? Should we not be aiming for higher efficiency in these vehicles? If tests aren’t accurately predicting usage, should we not develop more accurate tests?

How is it misleading?

Manufacturers make claims about fuel consumption. Based on studying real-world data, fuel consumption is significantly worse than claimed. The study authors say that internal combustion engines are active much more frequently than claimed. They propose that manufacturers and regulators use real-world data because it’s more accurate. Is that such a bad idea?