I wouldn't necessarily have a hard time believing Alexander Blade really is one guy. There's much larger projects out there that are explicitly known to be "one man shows".
Either way, all I know is the manner in which major GTA mod software like ScriptHook (and also, notably, OpenIV) is closed source contrasts with equivalent software for just about every other "very popular" game I can think of, which is pretty much open source across the board.
E.G. with OpenIV, I'd love to take a look at the source to figure out just why exactly it insists on installing itself in one very specific folder, on the C drive, which I find to be an odd / annoying limitation. It's like, come on, what are you, Visual Studio 2013 or something?