Ciaffone says BDF is more dangerous than FD. Why?

[PygmyHero]

This hand is from Bob Ciaffone's <u>Improve Your Poker.</u> The game is PLO. The limit is not stated, but I think it's fair to assume mid / high. I also assume it's full ring live, though this is not made clear either.

Sorry for the sparse hand details - I provide all the information that the book presents (pg. 99 if you want to review). I don't think that will be a problem since my question is general, and not about this hand per se.

Preflop: Hero is on button with T [img]/images/graemlins/heart.gif[/img]T [img]/images/graemlins/diamond.gif[/img]6 [img]/images/graemlins/heart.gif[/img]6 [img]/images/graemlins/diamond.gif[/img]
Action before hero not stated, pot appears to be unraised.

Flop (pot size not stated): <font color="blue"> (Not sure how many players) </font> Q [img]/images/graemlins/spade.gif[/img]J [img]/images/graemlins/spade.gif[/img]7 [img]/images/graemlins/club.gif[/img]
Checked around.

Turn (pot size not stated): <font color="blue"> (Not sure how many players) </font> 6 [img]/images/graemlins/club.gif[/img]
Checked to Hero, <font color="red"> Hero bets pot, </font> 1 call, <font color="#666666"> everyone else folds </font>

River (pot size not stated): <font color="blue"> (2 players) </font> 9 [img]/images/graemlins/spade.gif[/img]
<font color="red"> EP bets pot, </font> Hero...

Ciaffone argues for a call here, thinking the villain is likely to be bluffing for the following reasons:
<ul type="square">[*]Turn action indicates villain has a drawing hand,[*]Some draws did NOT get there on the river, [*]Villain may think you were on a draw and missed, [*]The two tens in your hand cut down on villain's straight possibilities, [*]With the flush on board, villain may have bet less or checked with a straight, and
[*](Quote from book): "The flush that hit was the two-flush that came on the flop, when everyone checked. The backdoor flush would have been more dangerous." [/list]I'm not particularly interested in the play of this hand, nor whether people think the river is a call. I'm really only interested in the assertion Ciaffone makes that the backdoor flush draw getting there would have been more dangerous than the one present on the flop. Can someone explain the rationale behind that?

*Edit: I just noticed this is PLO, not PLO8. However, I don't know if that affects the concept I'm asking about here. I don't play Omaha high, so I'm interested in this as it applies to O8OB. Which flush draw coming in is more dangerous - the one on the flop, or the backdoor?