He is right in that they never poured the dam in such massive sections. If they would have poured the dam in one giant slab it would have taken over 100 years to cool and cure. They actually ran steel pipes through the dam and pumped coolant thought to speed the process, also they poured it in thin sections, only a few feet at a time, maybe less, that is what I am not sure about. No one probably got buried but I bet they could have if they wanted to.
Maybe not though, the way the rebar and cooling tubes were laid in there could have made each pour only inches thick.
That is the highlight of going to Vegas for me, (beside the booze, strippers, gambling, etc.) pretty much every time I go down there I try to make a trip to the dam. That damn dam blows me away every time I see it.