He says the rulebooks are a mess, and that people having fun playing AD&D 2nd ed are selecting from and/or adding to the books to create the actual game they're playing.Early on he lambasts AD&D 2e as being a mess, basically calling it garbage.
This actually relates to @kenada's point about design. A lot of published RPG books take it for granted that the players of the game will build a good chunk of the process of play themselves. Gygax and Arneson got away with this, because they expected their readers/players to bring tabletop wargame intuitions and procedures to the table. But it's weird that RPGing has stuck to that paradigm - of presenting incomplete rules texts - for so long.
Not universally, of course, but in many cases.