[derefr]

You're thinking of having 50 attempted hobbies that you pretend you'll get back to one day. (I know; I have ADHD too.)

But McCarthy meant that he had 50+ concurrent consistently-actively-pursued hobbies/passions.

Which is something that's possible... if you have a lot of time on your hands, and you never allow anything into your life that drains you mentally so much that doing it kills your motivation to do anything else for the rest of the day. (Which IMHO is really only an option for people who are either retired, "independently wealthy", or being homeschooled.)