Unfortunately you are making it personal! Just stick to the facts?
Nobody in Thailand knows all the laws, even, especially the police!
How can anyone expect a tourist who is on vacation to know everything? However the captain of the boat should definitely know and should have explained to the tourist, what he can and cannot do.
The tourist is at fault and should be punished, the captain is also at fault and should be punished.
But 5 years in prison?? That is not reality, even in Thailand!????