[MrFizzbin]

It's an honest mistake on the other players part, you could have asked for a count before the call to make sure but you didn't, and if you had its not like the extra hundred would have made you fold would it ?

If you had won and counted that there were 6 bills instead of 5 would you have let him keep the 1 he didn't tell you about ? if so then the ruling is right, if you would have kept the extra 1 then you should have paid him.