Nanase is HYPED!
George is enough of a loner that I wasn't big on the idea of him having a lot of firsthand experience actually playing the game.
From my own firsthand experience, however, I know a lot of interest in these games can exist even if one doesn't play, and depending on who you listen to, a lot of the rules can be known secondhand. What's more, one might read the books and have familiarity with the rules without ever having played.
So possible minor spoiler here, but he does know the rules well enough to make good on this offer. This is less "dramatic plot twist" and more "yeah, this would be in-character for George".