That's a horrible flop to raise. Compare to
this hand and the reasoning is largely the same; the hands he wants to fold out aren't folding and the hands that he can beat are mostly giving up once he calls the flop anyway. Except, of course, that Durrr knows how to fire 3-barrels with air.
The river call isn't quite as amazing as some of you make it out to be. His river range is polarized. He'll have a set some of the time (although discounted since he didn't 5bet preflop; he likely would have with kings and queens, at least, given that Ivey is unlikely to flat AA and KK after someone else had already flatted a raise) and AJ some of the time, but his value range isn't terribly wide. Ivey gets ~2.5:1 to call the river, and I think what ultimately tips the scale to a fold is that Durrr could be turning a better hand than A6 into a bluff (e.g. 77/88/99 or T9). That's why AT is a stronger bluffcatcher than A6, and I think AT (assuming he would have gotten to the river somehow with it) would have called.
It's rare that I bother watching these shows because most of the time it's celebrity tournament players who quite frankly aren't that advanced in their cash game who like to splash around, but Dwan and Ivey are great fun to watch.