That’s very flattering!

A big part of it is that I’ve worked hard to have good research skills, so if I get sent an obscure question – like that one about House Osgrey of Leafy Lake – I go straight away to asearchoficeandfire to find every time the key words show up in GRRM’s writings (before that I would do word searches in my Kindle versions of the books, so asearch has made my life MUCH easier), then I go to the Wiki of Ice and Fire and Tower of the Hand to look for context so I don’t miss any pieces of the puzzle. And if that doesn’t work, I know a lot of smart people like @goodqueenaly or @warsofasoiaf or @poorquentyn or @nobodysuspectsthebutterfly or @joannalannister who I can bounce questions and ideas off of. And if it has to do with history instead of ASOIAF specifically, one of the things that eight years of grad school has taught me is how to research historiographical issues in a hurry by consulting JSTOR and doing the right keyword searches in Google Books and Google Scholar, etc.
Another part of it is that my brain is wired in weird ways. I have a hard time remembering things I directly experience – someone’s name, what I needed to get from the shop, etc. – but I have a really good memory for anything I’ve read, watched, or listened to. Character names, dialogue, plots, lyrics, stick in my mind for years and years, in part because the way I remember this stuff is by constructing fictional “historical narratives.”