Drivers likely could not give an accurate estimation for how many feet it takes to do anything on the road, such as come to a stop in an SUV going 50. Given the extreme mass of a cargo train, I wouldn't be surprised if the distance figures sounded high.
Isn't knowledge of stopping distances for vehicles at various speeds and different road surface conditions a requirement for obtaining a driving license? (At least, in the UK I believe it is, and I think the Highway Code tables probably over-estimate these distances for safety purposes)
That said, I think often the bigger problem is people not realising especially in more unusual conditions (like snow in much of Britain) quite how much longer braking distances become.