You can pick and choose which articles to quote as to how much glycogen an 'average' male may store when rested and well fed, but even taking the lowest estimate of 300g carbohydrate stored, it just doesn't make sense to 'bonk' on a day hike unless something is pretty out of kilter. Unless you are exercising very intensely, you are almost never burning 100% glucose for fuel. At 50% VO2 Max you are probably burning around 50% CHO and 50% fat. So that means 1200 calories from (stored) carbs and 1200 calories from (stored) fat if you ate nothing during your hike. When carbs get low, your body will then move into gluconeogenesis, from fat, protein or both. Marathoners 'hit the wall' because gluconeogenesis and absorption of carbohydrates from food cannot keep up with the burn rate, but this doesn't seem to be greatly affected by duration, only distance (the famous 18 mile crunch). But they are usually running at greater than 50% VO2 Max, probably closer to 70%, thus burning a higher proportion of glucose compared to fats (around 70% carbs/30% fat). That is assuming you are not 'fat adapted' to exercise.
However, another thing to consider is that hiking uses mostly legs muscles, and neither glycogen nor intramuscular triglycerides can be shuttled from, say you arm muscles, to your leg muscles. Same with running. In any event, it is not 'normal' to run out of glycogen/glucose that quickly, and you certainly would not see things restored that quickly with a meal of only protein and fat if you had run out of glucose. Jack may have experienced a reactive hypoglycemic episode on his previous hike, but the rapid recovery in the absence of simple sugars points more towards gluconeogenesis (i.e. a rest) making the difference than the food he ate. If jack is a reactive hypoglycemic then there is no doubt that eating less carbs will probably help, both his hiking and long term health. As I've mentioned in other threads, I am a real big fan of knowing rather than guessing, so would be inclined to carry some blood glucose test strips and see what my glucose levels are really like if that happened again. It won't tell you what you insulin levels are, but if you are not shooting insulin and you become hypoglycemic, it's a pretty good indicator of insulin resistance (or exercising at a very high intensity or a prolonged period of time).