Long story short he got lucky in the 90s with an inheritance and a publisher and can now devote his life to researching and publishing English slang. It's also interesting to me because it's a project that started as a book but has now migrated successfully to the Internet, both for publishing the dictionary and for doing research for updates to the dictionary.
It's interesting reading them as a native speaker, as there's so few that I could even begin to guess what they mean.
[0]: https://www.telelib.com/authors/O/OrwellGeorge/prose/Downand...