By that time he'd already created the foundations for game theory with his minimax theorem of zero-sum games. I think its more likely that he knew was he was doing and expected to lose the money.
Old roulette wheels had large flaws, even in the 1960s: https://thehustle.co/professor-who-beat-roulette. 30 years earlier they must have been worse. So there is a chance he noticed some anomaly that he tried to exploit.