My wife is Japanese and she taught me that a sweet tomato has a peculiar smell if you hold it close to your nose.
You need to learn the smell, but the best I can describe is that it’s an earthy smell. Very distinctive.
So this knowledge is relatively unknown in this country.
I've never heard this one before. You learn something new every day!
Here's a link to an article that might be related to this:
https://www.livescience.com/27349-smells-influence-fruits-sweetness.html