They could cheat in a lot of little ways. The caddy's could have been marking the score cards or it could have been something much less noticable.
For example - under the rules of golf you have to hit the same ball throughout a hole but some balls are designed for long straight flight (which is good off the tee) but they are less than desirable for short shots near the green. If a caddy picks up the ball they could replace it with a "softer" ball which would be better for short shots. Doing so would be a violation of the rules of the game.
Likewise, a shot that lands in a sand bunker often burrows into the sand. That make sit hard to hit out. A caddy could check the ball though (just to verify that it is the correct ball of course!

) and when they put it back down they could set it "up" on the surface of the sand which would be easier to hit out of the bunker. The same sort of thing can be done when a ball is hit into "the rough" (longer grass off the main fairway).