Sorry SRT.. but the issue is "possession". If you put two guys limits in one bucket and you're carrying the pail then you have too many fish in YOUR possession. Many have been nailed walking off Simcoe ice in that situation.
"Party" fishing is simply a term for doing what he admitted he was doing. Attempting to fill 3 peoples limits by catching and keeping more than his own personal daily limit.
I can't comprehend what anyone was able to prove wrong with that diagnosis, in accordance with Ontario Regs, in this situation.