This paragraph is specific to what happens when you bonk - what it means is that when you bonk, you go from a mixture of carb and fat metabolism (with the ratio dependent on how hard you are exercising and how well trained you are) to all-fat metabolism, because you have no carbs left.
Many cyclists describe bonking as the "outrunning of availible glucose" due to prolonged high intensity efforts. Athletes often have the will-power and capacity to work themselves into medical emrgencies due to very low blood glucose levels.
Decreasing intensity, switching to fatty acids or or other energy substrates to supply glucose is known as "getting tired," or running out of gas. It is not bonking.....
This thread starter, as well most of the public generally confuse any change of blood sugar at all as a
bonk. Trained athletes seldom suffer, nor react to slight dips and highs in blood sugar, they just keep working.