3 players in the hand 1 disqualified

[Buckeyes]

Cash game, Hand goes to the river. Player A bets 20 Player B calls and Player C raises to 120...... Player A then goes all-in for 675 and before player Player B can call or fold his hand Player C turns a card over and shows the table. Floor is called over as table erupts. After 5 minutes of sorting out what happened floor rules Player C has a dead hand and gives a warning that if it happens again Player C could be asked to leave. Note that there was two 3's on the board and the card Player C showed was a third 3. Floor also said that if it were a tournament the hand would not of been a dead hand.

Was the ruling correct in this situation?