This was before established science took a look at it? Or were the guys who started bodybuilding just extremely lucky to guess these numbers?
Not sure of what came first, the science of the workout fanatic.
Poliquin takes many things into consideration. He does his own studies with his lifters. Oversees other lifters from other coaches he advises, talks to and discusses things with. He will also study medical journals (he
says he is an M.D., but doesn't use the letters after his name as he feels it's highly overrated) or whatever possible medium that allows him to further knowledge.
So I guess to answer your question, it's not based on one thing or the other, just pure experimentation with the results reported as to what was found at the time.