200NL - puke and fold?

[adMIT defeat]

This hand was live at Foxwoods.

Hero ~ $350
Villain ~ $400

Table has been extremely loose with an essentially constant live straddle. In the only significant hand Villain has played, he flopped a set under set (555 v 777), got all-in on the flop, and caught quads on the river.

A few hands later, this hand played out:

Preflop: Hero is dealt 5c6s on the button. (9 players)
UTG straddles, calls all around. Straddle checks.

Flop: (36$) 4d 8h 7s (9 players)
Checks to Hero who bets $30. Folds to Villain in MP who calls quickly.

Turn: (96$) 8s (2 players)
Villain checks. Hero thinks, then bets $50. Villain thinks for awhile, finally calling $50.

River: (196$) 2c (2 players)
Villain thinks, then checks. Hero considers for awhile, then bets $50. Villain instantly goes all-in.

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Does villain ever show up with a bluff here? ex. a pair and a spade draw?

Does villain ever value bet a non-boat 8?

The passive play up until the river seems uncharacteristic of a set. The play at the table has been pretty aggressive with big hands, so I'd expect him to come out betting (especially given the previous set over set hand).

Is this a puke and fold?