I'm guessing the distinction lies in whether you are fat-adapted or not.

In a person who is not getting any carbs (or a ketogenic level), the body adapts, up-regulates the fat metabolism and learns to produce enough glucose on its own for the needed brain function and the body learns to use other fuel (fat in whatever form) where it can. This person might be out of glycogen, but the body can produce fuel fast enough to support lower intensity long term exercise, like a marathon.

In a person eating carbs, the body is going to use glycogen & glucose for fuel and won't be ready to convert fat to fuel efficiently enough to pick up the slack when the carbs run out. Hence, the bonk in a marathon if you don't keep providing carbs to the body.

My understanding is that it's the shorter distances (100 meter dash) where the energy requirements are so quick and so intense that the conversion of fat to fuel is too slow to work, even in those fat adapted. Without the very fast acting glycogen and glucose, you can't keep up. It wouldn't be that you couldn't do a 100 meter dash, but you'd quickly run out of steam and wouldn't be able to match to lightening fast intesity of the carb fueled sprinter.

But you have to compare apples to apples, not apples to oranges. Of course a fit, strong, completely fat adapted low-carber can still lift weights, but would he be able to lift faster & more weight if he was the same person and carb-adapted?

At least that's how I understand it.