I doubt the diet has anything to do with it. (In this case anyhow... certainly nutrition is critical for harder efforts).
Anecdotal reference point: I go out every weekend with 3 friends, we do minimum 3.5 hours riding time in the local mountains, and the most any of us eat is something like a cereal bar and a banana. I can count on the fingers of one hand the amount of times any of us have bonked in the past 5 years...
I trained 400 - 500 miles per week, riding anywhere from 10 to 140 miles per session. I'm 40 now and still cycle but just for pleasure and getting around now, slower than I was before but riding centuries is still no problem.
In short, I know exactly what the knock feels like.
I expect you are carb loading either the day before or in the morning before your rides, and that could easily give you enough stored glycogen to see you through a 2 hour ride.
I however was cycling to burn off fat that I'd built up during a few months of strength training, so the last thing I'm going to do is gorge on pasta the night before.