People have thrown weigh-ins in the past, but usually as a strategy towards winning. For example, someone would win immunity in a challenge. Since they don't have to worry about getting kicked out, they drink extra water before the weigh in. That way, they have extra weight loss the following week.
They have added a rule about immunity in recent seasons. They say the immunity is invalid if the contestant gains weight. Now they have to be more careful how much they drink.
What gets me is they always deny it and act surprised. If it was me, I think I'd fess up and just say "I drank some water because I had immunity. No sense dehydrating myself for a weigh in that doesn't count against me." Or even this dude could have confessed that he missed his family and wanted to go home and finish his weight loss there.