This seems like a flawed argument. By the logic in this article, wouldn't horses or cows, which weigh multiple times what a human does, have to have stocky rather than slender legs?
How big is big?
The practical limit for bipeds is probably ability to survive a fall to the ground. It's not super common, but enough people die simply from falling from standing.
1. They stand on 4 limbs, rather than 2.
2. That would be assuming that human legs are sized at the max capacity they can carry, which is not true.