Good common sense article. But you will be amaze how many people are not aware of basic knee care The knees are the most stressed and most used part of our body but yet most people ignore and abuse them.
That website misses the big picture. The human body is composed of many joints; when loaded it distributed that load through those joints. Consider this: what happens when the foot/ankle or hips are impaired in their functionality? Answer: The knees pick up the slack - and eventually they get overworked. So, let's consider what happens here: you strengthen your "knee muscles" so they can handle even more load. But, your body responds by shifting more load to your knees. You haven't dealt with the real problems like a lack of hip or ankle mobility. So, a big thumbs down on that website from me. It doesn't provide the real information needed to really prevent knee injury.
You cannot just strengthen the 'knee muscles' as what is consider 'knee muscles'? I don't think the web article imply that we should strengthen the 'knee muscles'. It make more sense that we should strengthen the muscles that stabilize the leg, i.e., the stabilizing muscles that hold the leg in the correct position throughout the full range of leg movement. I believe this is what the article meant when it said strengthing the muscles will reduce the stress on the knee as correct leg position will minimise the stress on the knee. When the leg stabilizing muscles are overloaded, holding the leg in the righ position is not possible.