Translation:Is it heavy?
Why duo hates kanji so much? Its completely reasonable to assume this おもい is 重い and not 思い but these are elementary school (or N4 level) kanji that everyone wanting to be anywhere near literate in Japanese needs to know. Chinese course however has a opposite problem as there is not pinyin, so it is not like duolingo's teaching philosophy focuses on spoken language. the Reverse tree has full kanji but the sentences are somewhat literal translations of English sentences and its sad to see "English is the most studied language in duolingo" when at least the Japanese course is so lackluster.
Why not is he heavy ? It depends on what you are talking about since it's not specified doesn't it?
I think both "is he heavy?" and "彼は重いですか" would imply "is he heavy to carry". This would make sense when carrying a kid or if you are working in the "garbage disposal" (or carrying a passed out friend or something). :-D But technically yes you are correct.
normaly you would just ask: "is he fat" ""かれは太いですか"
not 100% sure though as I'm not a native english speaker.
Another example was " he is a little heavy" so I think It should apply here too
I don't remember that example. But after a bit of digging. you are correct. However a heavy or 重い person is not necessarily weighty (both can mean important).
So yes "Is he heavy?" should be accepted. Duolingo can be a bit funky sometimes.