'He is hot' is slang for attractive so I would avoid this, grammatically it is fine which is why it's in the textbook but if you say it in real life you might get some weird looks. I'd probably say something more like "he looks too hot", "he looks warm" "He looks like he feels hot" or even "He look like he's getting sun burnt". Something like that just to avoid calling someone hot haha

You can say "He looks hot"... funny side note, we say this when someone looks sexy or attractive as well...lol

I think it's an attempt at humor: "If a man looks that hot, it's because of the weather." It's a play on words between overheated and sexy.

Best way to phrase a man who is in hot weather is "he is feeling hot" then shows that the weather is making the man hot. But the word hot is also an adjective for attractive. So you would say "he looks hot".

Thank you guys!