You can massively discount any bluffs even from an aggressive player like Brian Rast. It is very uncommon for someone to bluff into 3 players on a board that would be likely to connect with at least two of them (the preflop raiser checked and can be largely discounted).
Rast’s value hands that bet flop and turn are likely to be 2 pair +. More importantly, Walter is out of position and so calling the large turn bet for his straight outs when he is unlikely to get paid off when he hits is not a great idea. And even if he is ahead occasionally with his top pair (e.g. against a hand like QTs) he will almost certainly get bluffed on the river and will probably have to fold given how many value hands Rast has in his range. I’m guessing that in position Walter would often call the turn instead of folding.