K-high on the river; A rare bluff from me

[marand]

Villian is too loose preflop, but not terrible after the flop.

Party Poker 10/20 Hold'em (6 max, 5 handed) converter

Preflop: Hero is UTG with K[img]/images/graemlins/diamond.gif[/img], Q[img]/images/graemlins/club.gif[/img].
<font color="#CC3333">Hero raises</font>, <font color="#666666">1 fold</font>, <font color="#CC3333">Button 3-bets</font>, <font color="#666666">2 folds</font>, Hero calls.

Flop: (7.50 SB) J[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Button bets</font>, <font color="#CC3333">Hero raises</font>, <font color="#CC3333">Button 3-bets</font>, Hero calls.

Turn: (6.75 BB) 2[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, Button checks.

River: (6.75 BB) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font> ...

I very very rarely bluff on the river, but decided to here.
I would have bet any blank card (thought he was very likely to be drawing to either a straight or a flush).
Is this standard?
If he folds, does that mean that I bluffed with the best hand?

Thoughts?