KK facing push on 4flush board

Villain is loose over a small sample. How often is this a bluff?

PokerStars No-Limit Hold'em, $0.50 BB (4 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($23.05)
BB ($96.15)
Hero ($45)
Button ($23.70)

Preflop: Hero is UTG with Khttp://www.flopturnriver.com/phpBB2/...iles/heart.gif, Khttp://www.flopturnriver.com/phpBB2/...miles/club.gif.
Hero raises to $2, 2 folds, BB calls $1.50.

Flop: ($4.25) Jhttp://www.flopturnriver.com/phpBB2/...es/diamond.gif, 8http://www.flopturnriver.com/phpBB2/...iles/heart.gif, 3http://www.flopturnriver.com/phpBB2/...iles/heart.gif (2 players)
BB bets $2, Hero raises to $8, BB calls $6.

Turn: ($20.25) 2http://www.flopturnriver.com/phpBB2/...iles/heart.gif (2 players)
BB bets $5, Hero calls $5.

River: ($30.25) Thttp://www.flopturnriver.com/phpBB2/...iles/heart.gif (2 players)
BB bets $31, Hero...

It doesnt need to be a complete bluff for us to call here. Often our opponent is going to have a pretty random hand here and think that there Qh or something else is good and push. They also could be making a strange bluff which adds to our equity here against their range. We really cant be folding the second nuts to a PSB on the river without much much deeper stacks and a much better read on our villain.