flat calling the nuts ? just happened at the main event !wtf

[dang44]

John Racener Slow Plays Quad Jacks

There was 4,000 in the pot and {J-Clubs}{J-Spades}{6-Diamonds}{5-Clubs} was on the board. The {3-Hearts} came on the river and a player bet out 6,000, John Racener called. Racener turned over {J-Hearts}{J-Diamonds} for quads, his opponent mucked his cards and Racener moved up to 46,250.

what is this ????????????