It's not a myth. The distinction here isn't general body odor, which everyone has, but a specific gene (ABCC11, the same that controls for wet or dry earwax). Those with the gene have a chemical in their underarms and groins that bacteria feeds on, producing a stinkier odor.

Also, I've ridden plenty of crowded buses and subways in China and haven't noticed as much body odor as Westerners. So our anecdotes cancel out there.