Personally, I have never felt that "flat calling" with the 'nuts' is deserving of a penalty.
If it is someone really experienced, I am more likely to question their motives but it would generally still result in a warning and that such behaviour is something I would monitor going forwards.
You either do it because:
You're trying to cheat/chip dump,
You wish for information on your opponent and by placing in a bet that could see your opposition fold his hand, you lose that opportunity. Or;
You genuinely didn't realise your hand.
99.9% of the time, in my experience, it is the 3rd option and occasionally the 2nd.
You cannot calculate or pre-plan being in a situation where you have the absolute best hand and then go on to use it advantageously to benefit a friend/conspirator etc thus it would seem to me that we should therefore consider that the situation arises through error or a desire to gain information. You could also argue that is situationally beneficial to someone in order to exploit certain situations such as the bubble.
Irrespective, I am rambling:
We do not have a rule that indicates you forfeit the pot. I have no idea how that came to be believed, but usually if something sounds absurd - it probably is!
Thanks for the clarification. I was astonished that it was even suggested, but the noise was great.