The main activity that makes your body gain muscle is to subject it to exceptional amounts of work — that is to say, a lot more work than it is used to (combined with the intake of the necessary fuel to facilitate it).
It should be reasonably simple to understand that using your own bodyweight as resistance is a very inefficient means by which to achieve this.
Not only do you need to use weights to reach a level of efficiency, you need to also continuously push yourself harder all the time, or else your development curve will flatten.
I disagree. The only thing gymnasts do is use their own bodyweight and as far as athletes go in terms of endurance and pound for pound muscle strength they can not be beat.
Gymnasts are not at all as efficient about building muscle mass as body builders are. Gymnasts achieve great physical results in time, but nowhere near as efficiently as body builders do.
This should not come as a surprise to anyone — for gymnasts, building muscle is a means to an end, and they don't want to build any extra muscle as that just weighs them down. For body builders, building muscle mass is everything.
The whole point of the article was about health/well-being through exercise and my point is that the gymnasts strike a very happy balance between strength/fitness and well-being. Whereas body builders exceed a lot of bounds and maintaining that much heavy/slow twitch muscle mass can be detrimental to one's health.
Becoming a gymnast is not a realistic way of adding muscle mass, unless this epiphany strikes you at about the age of seven.
Even if you do decide to go the gymnast route, you'll still be lifting weights (though not until you've been at it for years, and you probably won't be making some newbie gym mistakes like prioritizing biceps), it'll just take longer to achieve results because you're mostly focused on acquiring the skill and technique to do actual gymnastics.
As for your other claim, body builders do not accidentally add too much muscle. It is a wide-spread fear among people who don't exercise at all, but it does not actually happen. You absolutely, positively, won't wake up one day and realize that you've accidentally put on too much muscle.
Accidentally putting on so much muscle as to be detrimental to your health would be akin to walking home from school or work and suddenly realizing you accidentally walked around planet earth and the soles of your feet have been completely worn down — you will not suddenly complete a journey that takes most people extreme dedication and hard work over many many years.
I didn't say go become a gymnasts. Anyone can do many of the conditioning routines gymnasts do to improve strength and technique. Push-ups, dips, crunches, v-ups, etc. are the most basic things most gymnasts do to strengthen their muscles and since most people are not going to be pushing boulders around I don't see a point in doing any kind of heavy lifting if you're exercising simply to reap the benefits of exercise.
Also, I didn't make a claim about accidentally adding too much muscle. I simply stated that the kind of muscles that weight-lifting builds is different from the kind of muscles you will build if you don't use weights. I've done both and simple routines that I can do at home exercise more muscle groups without isolating specific areas and overall I feel much better.
It should be reasonably simple to understand that using your own bodyweight as resistance is a very inefficient means by which to achieve this.
Not only do you need to use weights to reach a level of efficiency, you need to also continuously push yourself harder all the time, or else your development curve will flatten.