To be honest, the only thing wrong I see with this is that they accepted him when he was heavier, and never mentioned anything about his weight until now, AFTER he lost 30 kg. That's just messed up. If they had refused entry to start with, I would have understood that - if it says that you have to be in good health and whatnot to get the visa, and you're overweight, then, as bad as it is, that's a good enough reason to refuse them.
But to let him in, let him work, and then after 6 years and quite a considerable weight loss to go around and say 'Hey, you're not healthy enough', and force him to leave a good job, that's just plain wrong. I have to say, I'm glad to see that bureaucracy is as bad everywhere as it is over here. I thought we were the only ones where crazy stuff like that happens!