ok, it does matter about what rules you want to go by.
a lot of card rooms will allow a player to show his hand to another if and ONLY if the players are heads up, regardless of where they place them on the table (exceptions - on top of another players cards, on top of the muck pile - both are dead - funny too, if he dropped them on another players cards - BOTH hands are dead, ouch) .i assume, though it was not mentioned, that the player had his cards turned face up in this scenario, if they were face down then its a muck (of sorts - back to this in a minute).
this is a cash game rule and is only for heads up play...if there are been another player to act behind this person then the hand is dead (or heavily penalized) -dead in most Michigan
rooms at least, and about half of the Vegas ones.
as i said, most card rooms allow this, some do not and would either kill the hand, or penalize the player (but pay him if he won) which may include kicking him out, maybe for good.
if they were turned face down, they are mucked, however most card rooms allow hands to be retrieved from muck if 100% clearly identifiable and there is a good and fair reason for it to happen.
I have always been saying people must know the rules of your game before you go play live, this is the same for home games - find a rule book online, whether it be TDA, Roberts Rules, or WSOP
, or whatever, and let everyone know ahead of time what book you are ruling from. You should also have a dealer that does not play, and someone running the floor decisions.
I think in this situation the player has the right to still say call or fold, IF his hand was face up, this is how I would, and have, ruled it based on the rules we use at my card rooms.
Now most of the above is if it were a cash game. if this is a tourney then different rules apply. If hand was face up it is never dead, no matter what (again unless dropped on top of another players hand or the muck pile), and most rooms will consider it a passive hand - meaning he can not raise or bet with it but can call. after the hand is over the player will get a penalty of sitting out for 20 minutes or so.
A lot of players seem to think that if cards pass forward they are auto dead, but its just not true, sorry