It's true that Gygaxian Naturalism is more about worldbuilding - and notably, treating the game area like a living, logical area. But there's something more to it, especially this bit from Grognardia where the term was coined:What do you understand Gygaxian Naturalism to mean?
My understanding is that it means he tried to have the game world embody a certain self-consistent logic. For example, the trolls in one room of the dungeon having a food source of giant cave crickets in a nearby area. Or the extensive description of an ogre treasure horde in the 1E DMG, containing trade goods, furniture, furs and other items which would plausibly be the booty of their raiding and pillaging local villages and merchant caravans (rather than simply x amount of coins and gems). Or the layouts of the various lairs in the Caves of Chaos having functional rooms, like guard rooms, lookout points, sleeping chambers, there being children and women present in the lairs, etc. Or Frank Mentzer's classic example of having reviewed the manuscript for the Keep on the Borderlands and noticing that there was a ranking priest but the map was missing a chapel. So he added one. Allegedly other folks at TSR thought this was a bold thing for the new guy to do, correcting an oversight by The Illustrious Founder, and expected him to get slapped down, but so the story goes Gary agreed that this was an oversight and approved the addition.
In that passage I think Gary was using "realism" to mean strict adherence to fact or history (and mocking the idea that such is possible with a fantasy world) such as would often be expected by historical wargamers, and which some competitors (e.g. the makers of Chivalry & Sorcery) claimed to be attempting, with extremely detailed, "more realistic" rules.
In contrast, Gygax says (in Snarf's quote): "It does little to attempt to simulate anything either."The end result of this is that Gygaxian fantasy is a simulation -- a fantastical one, to be sure, but a simulation nonetheless.
So I think there is some inherent opposition between the two schools of thought. I'd guess that the gamist principles that Gygax espouses in the DMG more accurately reflect the Classic tradition in the hobby, while Gygaxian Naturalism is more in line with the Trad school of thought.