There is a lot of widespread knowledge describing in detail how the cars drive and behave, videos and in depth articles, highly detailed driver explanations and even onscreen telemetry during lap footage, you can see in plain sight exactly what happens based on a drivers input. These are things that the simulators reproduce as you would expect, predictable results over a number of different simulations, results that a motorsport book or a racing instructor could tell you to expect. So when something shows up that does not conform to the norm and is very different to the results that all of the others achieve then you suspect it is wrong.