"At the highest intensities, the fastest athletes expend about 1,000 calories per hour, with perhaps up to 60 percent of that coming from carbohydrate-based glycogen. It’s unlikely that all but the largest athletes consume that much carbohydrate. In fact, you don’t need to replace it at all if you did a good job of eating quality carbohydrate in the 24 hours leading up to the race or workout. If you did, you have probably stored 1,500 to 2,000 calories as carbohydrate in your muscles and liver, depending on your body size. By keeping the hourly deficit at less than 100 calories, even the elite athletes in the longest of these events—those who are likely to burn the most calories—can avoid bonking.
This may or may not be a quote from the book. It's unclear from the OP whether the above is a quote from the book or a C val quote from a paleo diet blog. In any case, it's necessary to understand what is being said and what not said.
If we work out the calorie budget for a typical stage, we can understand this better. Let us assume a 6 hour hard mountain stage, and a rider with full glycogen stores, 2000 calories (kcal., actually). The rider can have a maximum average deficit of 2000/6 or 333 cal/hr. If the rider were to consume an average of 250 cal/hr, the rider would be able to burn an average of 583 cal/hr for a total 6 hour burn of 583*6=3500 calories. That average output level is hard to achieve for most of us. But let us say it's a mountain stage with 15000' of climbing and say our hero averages 4000'/hr over the three major climbs. That's 3.75 hrs. of climbing and 2.25 hrs. of descending and flats. Suppose our hero averages 700 calories/hr. for those 3.75 hours, or 2625 calories, leaving only 875 available for the remaining 2.25 hrs or 388 cal/hr. That's his calorie budget. Teams have this sort of data on their riders. That's how they work out the stage strategy. Of course sometimes our hero just can't perform at this level, oh well.
More realistically for each of us, the same thing applies. It's hard to get that 250 calories/hr. down and keep it down. That's a major challenge, just eating enough. On a fast rando ride, the cyclist may ride 18 hours/day and won't have glycogen stores topped up after the first day. Even eating at the maximum level, average burn will have to be under 350 calories/hr. That's just pacing. OTOH, it's easy to see, as another recent thread here indicates, that the average rider can do a 4 hour hard ride and not eat much at all if they are in good enough condition to be able to ride fast at an output level that burns mostly fat.
Those of you with power meters and experience in metering out the effort can come up with better figures than I guess at here. "Titrating the pain," I call it.