You are mischaracterizing what he is saying.
Your body is capable of glucose through
Gluconeogenesis. For activities where the
rateof glucose use does not exceed the ability of the liver, kidney, and intestine to produce it then your performance won't suffer. However, in high intensity activities where the rate of glucose consumption by your body does exceed that rate (like sprinting and weightlifting), then your body will need to draw on
glycogenthat is stored (mostly) in the liver and muscles. Exercise with high intensity frequently enough and your body won't be able to store enough glycogen in your liver between training sessions and performance will suffer.
Note that endurance activity uses glycogen as well, just not as much as quickly.