i think bodybuilding is a bit different from other forms of competitive sports.
Those committed to bb, inlcluding those who do not compete for a variety fo reasons, adopt a lifestyle which consumes their time and energy enough for them to legitimately call themselves bb's. In this sense, bb is also a lifestyle, and art, and a competitive sport if he or she chooses to take the ultimate test of going on stage before their peers.
All people around them also consider them to be bbs, just looking at them and observing their dedication in terms of diet and so on.
I did bb for a few years, but never competed. I sort of knew i would look quite skinny at a ripped 90kg on a 186cm frame.
In contrast, i find competiting in running, throwing, powerliftign and olympic lifting much less daunting.
Hope this makes sense.