Odd rule call for LLWS 2016 - dead ball...how many bases umpire?

Playing at the Little League World Series there are ground rules for that baseball field like there are for every field. In this case, there is a unique play that causes a "dead ball" call and runners placed. The commentator wonders allowed why they only advanced one base and didn't advance two bases based on the rule book. See our updated video posted Dec 2018. VIDEO UPDATE:    • Odd rule call for LLWS 2016. Dead ball. Ho...   The answer rests with the field ground rules which, apparently, state that when a thrown ball hits the flat area of the fence behind home plate (causing the ball to bounce straight up rather than back like it should) then the umpire is to call "dead ball" and advance the runners only as far as he deems they would have advanced had the ball hit the back stop cleanly. Therefore, the two base rule is not in effect as the ball never does leave the playing area. It is not thrown into the bleachers or dugout area. This ground rule is to protect the integrity of the play since fields normally do not have a flat "shelf" like area behind home plate.