I think the distinction Bluedevil is trying to make is you're going into this SaaS app with no intention of it being hugely profitable or successful. You're scratching an itch and if other people decide to pay you to help scratch their itch as well, then that's just a sweet bonus.

In contrast, a business would be going in with the intention of the service/app being successful (profitable or popular). Maybe hobby isn't the best way to describe it, but I agree your way of looking at things is closer to a hobby then a business.