go on then - where was it hidden
If i was the TD i would ask why did you turn your cards over. If im told its cos i thought he was all. i would then ask where was the chip that wasnt allin. If im told its cos it was in his hand and not on the table i would have the common sense to realise this was either a genuine mistake by both parties or angle shooting.
If im told it was the guy with the 1 chip in his hand id

him for taking chips off the table during a hand and award the whole pot to the other guy.
If someone has pushed all of their chips past the line and someone has called and then turned over their cards, you need to look at the situations on a case by case basis. Every situation is different and it's a matter of applying common sense.
First and foremost, it's a tough situation for TD's and rulings will always be given incorrectly. In my opinion, the TD needs to analyse a few things.
1) Why did the player table his cards.
a) Because he wanted to expose his cards for some reason.
b) Because the player thought they were on their backs, having seen the player push all his chips in.
He needs to know key information from the dealer here. Particularly whether the last single chip left behind was visible or held by the player. If it was hidden, then the player is at fault for hiding his chips and I would say no further betting to take place and decide the winner of the hand from that point. The caller has called believing it to be all in and clearly the player that has hidden a chip is at fault for hiding his chips. I would ask that he table his cards also and in future make sure every chip is on visible display to all the table. It is his responsibility to do that.