Prematurely tabling cards in MTT

[mxp2004]

In a tournament yesterday at the Borgata, Player A prematurely tabled his hand on the river before Player B had a chance to act. Before Player B could see what was tabled, the dealer covered Player A's cards with his hand. Player B then made his action, and the hand was completed.

I was not involved in the hand, and so I kept quiet. But did the dealer act properly? In other words, once a player tables his hand, even if done prematurely, isn't the hand now exposed for all to see regardless of what action remains?