There is a correlation between the cross-sectional size of a muscle and its strength. Larger muscles are pretty much always going to be stronger than similarly strength-trained smaller muscles. The scenario in that link is plausible for a bodybuilder preparing for a competition who has dehydrated and starved himself to get very low body fat. A well-fed strength-trained individual could very easily be stronger than a bodybuilder in that point in his training, despite appearing to be smaller (low bodyfat always makes one look bigger, though). However, there are obviously lots of factors that affect strength, so to even the playing field, let's suppose we took two muscles and strength trained them equally, so that they are able to generate the same amount of force, then made one muscle magically bigger. The bigger muscle would actually then be more effective at moving bone around a joint - effectively being stronger. This is because the muscle fibers have a much greater 'angle of attack' when they contract; the fibers now have many more angles to pull against the tendon, versus a smaller muscle which has a much smaller 'choice' of angles to pull on the tendon.