This considered an angle shoot or a bluff?

[HotPockets]

I'll do my best without a converter, but i'm curious if anyone has seen this before as I can't decide if it was an angle shoot or just a sick bluff.

1/2NL at Borg

Two players are heads up on a flop of 6 [img]/images/graemlins/diamond.gif[/img] 8 [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/club.gif[/img]
Tight Old Guy bets out about $15, and solid player raises to $50.
Both players have around $300 or so behind at this point.
Turn is 7 [img]/images/graemlins/heart.gif[/img]
Tight Old Guy checks, and Solid Player Bets $100
Tight Old Guy quickly says, "I call, I have a Straight" and starts to turn over his hand.
Dealer stops him and explains, there's one card left to come.
River is a blank
Tight Old Guy shrugs and says "I guess I'm all in then"
Solid Player mucks set of 6's face up and Tight Old Guy shows him King High and rakes the pot.

Is this Kosher? I'm not really sure how I feel about this