So, you guys were actually discussing energy output instead of energy consumption? Now the earlier comments make more sense but it's still a weird way of looking at it. Though if you have a power meter then it's an accurate number on actual output. Going ahead you should probably clarify what you mean by a 500kJ ride. As in the energy output of the ride was 500kj and the assumed energy expenditure was then 2000 kJ.
So the 4km world record was achieved with 150kj. That is energy output. The actual energy consumption would then have been 600kJ. And if we assume an efficiency of 25 % that then converts back to roughly 150kcal energy consumption, which is quite a lot for four minutes of effort. An hour at that effort (impossible obviously) would then be 2250 kcal or 9414kJ.
I also have to emphasize that saying that 2500kcal is 2500kJ seems like the peak of idiocy if you have not clearly outlined the context in which that statement is uttered. Even on a cycling forum, without the context of output/consumption outlined beforehand it's just pure nonsense.