While they do show it live, it's in the middle of the workday, so almost everyone in the USA will have watched it delayed by many hours at "prime time", aka around 8pm local time in each zone.
That being said, I'm in the US and I heard boos on the delayed broadcast.
Oddly I watched it live on the Eurosport broadcast and didn’t hear any noticeable booing
as I unterstand the boos were blotted out only on the NBC broadcast, did you watch it on NBC?