Show Cards = Dead Hand. OK Ruling?

[WindedAorta]

Home Poker NLH Single-Table Tournament.
4 players still in.
On the river, Player 1 bets. Players 2 (me) and 3 are already out.
Player 4 shows his cards. He has (AJs), a busted flush draw but middle pair (there's a king on the board).

I (the dealer) start to clean up the cards for the next hand. Player 4 pauses for a bit, and protests, saying he hadn't folded. (By this time I've given most of the chips to player 1 and he's mucked into the pile of cards)

I'm the rules authority for the tournament, and I say the hand is dead, because player 1's hand was still live.

Later I do a little research with Robert's Rules of Poker, and see that:
21. Showing cards from a live hand during the action injures the rights of other players still competing in an event, who wish to see contestants eliminated. A player in a multihanded pot may not show any cards during a deal. Heads-up, a player may not show any cards unless the event has only two remaining players, or is winner-take-all. If a player deliberately shows a card, the player may be penalized (but his hand will not be ruled dead). Verbally stating one’s hand during the play may be penalized.

Fortunately, rule #1 in our tournament is "The Tournament Director is always right, even when he is wrong." I'm the director (even though I'm playing). Nobody has ever complained about that rule (and all the players in that situation have played with this rule many times), so I assume nobody thinks I've ever taken advantage of being the final arbiter (I let others make the ruling when I'm in the hand, but even when I'm out rulings can still affect me a little so long as I'm in the tournament).

But did I make an OK (in your opinion) call? This is a casual little home game but because most of us also play in casinos we try to stick to the rules as much as possible. I made the ruling partly because I don't like the kind of action Player 4 made, trying to get a read by showing Player 1 his cards. Also partly because Player 4 let the cleaning of the board go just a little too long to stop us.

Would it be OK (in your opinion) to add the rule to our home game rules? Intentionally showing your cards makes it dead? I'd rather not complicate our home tourney by adding pentalty rules.

I think it would also help if we had a real poker table with a line instead of a normal table. Mucking cards would be much clearer. We're pretty sloppy even when it comes to how far your bet had to be away from you and such. Sometimes the bet is only 2 inches from the stack.

[Lottery Larry]

I agree with your ruling. However, add that to your rules, in whatever format is game-friendly, as soon as you can.

[kodonnell]

I host a weekly game with about 8-10 players per week. In my game, showing your hand does not make it dead. You may get called some names though. If you do make the ruling that way, you should make sure everyone knows it when they enter.

My worst habit is exposing my cards after the betting before the river (usually intoxicated). I never mean to, and it is way to my disadvantage, but I would be way upset if my hand was dead.