That's insane.
When I was a teenager I swam competitively, and I could swim underwater for about 2.5min without surfacing but that was just lengths in a swimming pool, not straight down, which is much harder (you have to fight buoyancy). I think I could cover max maybe 70-75 meters at my best, he's going well over twice that (98m two ways) and doing it down and up rather than back and forth.
It's a lot more dangerous to go down too, obviously, if I couldn't make the length I could just surface and breathe, he's GOT to make it or he dies.
Swimming underwater is a hell of a lot harder than just holding your breath because obviously your muscles have to burn oxygen to propel you.