Early in tourney

[Melchiades]

Early in MTT $10+1 NLHE.

400+ players, it's my first tournament of this kind and I'm pretty new to this so I'm probably out of my league. But one time has gotta be the first.

Table is pretty tight and passive. I've doubled my stack by mostly betting on the flop with everyone folding.

So here's the situation:

I'm on the button and I am dealt [Qc Qh]. Blinds are 10/20. Everyone folds to me, I raise to 80 as I've done a few times before with usually just the BB calling or no one. SB and BB calls.

Flop comes [Qs 9d 8d]

Both check and I make 2xpot bet. Logic being that one or both might be on a flushdraw or straightdraw and I want them to have bad potodds for calling. SB folds and BB calls. Turn comes [4d]. BB bets a half the pot bet or so, what do I do?

I went all in thinking that he probably didn't have the flush since in my mind that would have made his call pretty bad. He calls river comes [As] he has the flush, my stack is almost gone and I go out a couple of hands later.

This guy went on to come 2nd in the whole thing so he probably knew his stuff. Why did he play like he did, and what should I have done here?

[Melchiades]

Hope I'not breaking forum etiquette here by bumping my own thread, but guessed it would be better than making a new thread.