First off, people with hyperthyroidism generally have increased appetite because of an accelerated metabolism, not reduced appetite. So half his symptoms already don't match.

Secondly, don't try to diagnose people over the internet based on half a symptom and today's weather. Suggest them to see a doctor and leave it at that.

Just because you happened recently read of one random disease out of millions doesn't mean everyone has that now. You'll cause more harm than anything.