I've trained with some dudes that love bragging about the big doses they take...dummies 
I think it depends on the individual. There are some who brag about their usage as they feel proud about it, probably thinking it makes them look more "hardcore".

I think others like John may feel more ashamed about it so instead choose to downplay their usage and the importance of drugs on the whole. He knows he can't claim natural and be taken seriously so he does the next closest thing - claims to be a very mild user. Lee Priest does something similar.
I think since John likes to emphasize the importance of training and diet, he feels that admitting the truth about the drug aspect will take credit away from the those previous two aspects.
Looking at John’s physique though, he certainly doesn’t have the look of a moderate user. A shitty structure but A LOT of dense muscle on it.