you saw two people wagering on anything besides the typical bets (poker or what not).
players may bet what the suits are in a flop, or if someone had a full house or not, basically stuff about the game but not part of the game.
say two people are playing poker, the waitress walks by with a huge tray of glasses, they may make a bet on if she will drop them or not. also maybe a player bets another they cant do 50 pushups in 60 seconds...whatever the case may be one person propositions another in a bet.
just gamblers being gamblers