Even though I've spoken fluent English for decades, it's still only my second language and I'm always learning new things about it!

Personally I had never thought of "smart home" as a compound word, but rather as a qualifier and a noun. It's a home that happens to be smart. Similar to "blue sky", or "hot dishes". In my mind neither of those would be hyphenated.

It's different from "man-eating", since that's not an eating that happens to be man, so in fact the whole word only makes sense as a unit in any sentence that would use it.

Clearly, I need to adapt my understanding! :)