The problem with people who think calisthenics can't put good muscle mass on a person is, the average, lazy person is doing about 80 - 100 reps each in pushups, pullups and situps. That's not going to do anything for you.
These guys at Wingate Park (BK), Lion's Den (Harlem) and other staples for calisthenics, they are doing 2,000+ reps total in pushups, pullups, dips, muscle ups, and other exercises, with added weight involved either with vests, belts, chains, plates, etc. 3 to 4 days a week. Natty or not, that's some serious work being put in.
Some of these guys are also well-known, like Giant (if anybody ever read the incredible but sad article on Dasani Coates, Invisible Child, he is in it). Matter of fact I'm gonna end this here and drop the link to the article, it's a few hours to read, but well worth it.
Invisible Child: Dasani’s Homeless Life