I'm assuming there were tee markers and they were playing whatever color that tee marker is. If the Tee Marker was set on the wrong tee box compared to the scorecard then that is the fault of the tournament. If they played a different colored set of tees then that is the players fault. Also the players fault if they played and empty box where the yardage should have been and not the marked tees.
Had a similar situation in a big skins/ 2 man best ball game in December. It was the last day that the course was open as it was sold to a developer. My buddy won a big city tournament there last summer. The skins game was full but the Head Pro was able to squeeze us in about 30 minutes their tee block with a couple older guys who had been playing there for years. We pull up to the 6th hole Par 3 and the tee markers aren't there on the box. He called to Pro who said to put something down from where we teed from and he would come out and get it fixed. We tee off and he shows up as we are driving away. We get about 60 yards ahead and look over to see the tee markers on another box. They were about 3 boxes and 60 yards ahead of normal (playing like 90 yards instead of 150). We took them back to the pro at the tee box and he was like yeah those shouldn't have been down there. Glad we were the first ones through and got it straightened out before any other groups played it.
Had a similar situation in a big skins/ 2 man best ball game in December. It was the last day that the course was open as it was sold to a developer. My buddy won a big city tournament there last summer. The skins game was full but the Head Pro was able to squeeze us in about 30 minutes their tee block with a couple older guys who had been playing there for years. We pull up to the 6th hole Par 3 and the tee markers aren't there on the box. He called to Pro who said to put something down from where we teed from and he would come out and get it fixed. We tee off and he shows up as we are driving away. We get about 60 yards ahead and look over to see the tee markers on another box. They were about 3 boxes and 60 yards ahead of normal (playing like 90 yards instead of 150). We took them back to the pro at the tee box and he was like yeah those shouldn't have been down there. Glad we were the first ones through and got it straightened out before any other groups played it.