Seems like his left testicle has not yet descended. Doctors say no sweat, in these cases, it usually descends later. If not by one year, then time to cut.
Annie has started calling him “Nong Kai Diao”, or “Little Brother One Nut”. While it’s funny as shit, I discourage it because I don’t want some neighbor to remember that in 10 years and then blurt it out in front of his friends.