There's a handful (maybe 2) people in my 41 years of training that would pass as a juicer, but never saw a steroid or supplement in their lives.
Hard training before, during, after puberty outburst is the main reason. One kid (now deceased in an ATV accident (thru the ice drowning) was a buddy who trained with us back in 1982/83 in our friends garage gym.
Dude was a skeleton. bUt when puberty hit (we were all like 13, and we all blew up) but this kid just had the sickest genetics. Muscles popped everywhere, huge tricep striations, tiny joints, big muscle bellies, etc.
We didn't know what a steroid was, there were no supps back then, and we were all 13/14 in 1982/83, so yes, very natty. Another was a buddy just like that one, same sort of skinny frame, tiny joints, and muscle bellies that would pop. When he would stop of course he would deflate and look scrawny again. This clown didn't even know what a pro-hormone was.
So there are some (probably very few) out there. This kid in the vid, who knows, specially now with easy access to anything they want. (Gear, peptides, hgh, etc).