I know a few other people that do similar things. Like a 15" RTC in a 20 gal. It's useless to say something because I know it won't help, as much as I hate it.
I strongly disagree with keeping fish like arowana's in tiny tanks. It's no good saying it looks happy because if it has no room to swim it's most likely not and saying they don't need space to swim to be healthy is daft. All animals need exercise to stay healthy.
I'm not saying you should go preaching to this guy but you definitely don't want to copy what he does. In my opinion it is cruelty and you where shocked for this reason.
I've no way of proving this but this is so wrong, we dun see any defect doesnt mean there isnt any.
Like a human or dog, you keep them in a toilet from baby till adulthood, they wont die but I think definite some impact will happen, lack of exercise? psychology (not sure if fish has them)? stunt? shorter life span?