How much music theory knowledge does John Mayer have?

Ive always been obsessed with how john Mayer plays guitar and how he writes his songs and thinks of his chord progressions, and the chords that he plays, and I wondered how much theory does he know? I saw an interview with him and he said he doesn't know how to read or write music and that he only knows a little bit of theory but he went to burklee for like a year so I'm confused.