Apparently exactly this. The people that I knew where always discussing the fitness of certain players and how that'd impact the game and stuff like that. Though it could've also been that they were on a long long lucky streak, because they minimized the risk with such considerations. At least t hey were not ruining their own lives
These sorts of inefficiencies, and often even true arbitrage bets, show up in sports betting because the bets you need to make are so complicated. There is a team at Susquehanna that does sports gambling as their form of trading, and they will sometimes play these sorts of arbitrages against bookies. I remember hearing about a perfectly-hedged arbitrage of 8 different bets from one member of that team in a specific gambling forum, but the bets were all so arcane that very few other players were playing each one.