Roon gets its information from the stream itself–we can pull name, description, and website link assuming the stream includes the right metadata. Not all streams do.
(We can pull even more data if you drop in a TuneIn link, of course…but I’m assuming that’s not what you’re talking about here).
We don’t have a radio directory/database. That will come in a future release.
We originally intended to wait on Radio until a directory could be built, but we got feedback from many users that said they would prefer to enter URLs + data themselves than to wait for us to build a richer experience–so we listened to the feedback and released the smaller feature with 1.2.