In Tribute . . . A Murry Moment

Playing the Poker Dream skins freeroll tonight when this little gem occurred.

I have a stack of approx 3,600.

I`m dealt QQ UTG+1, blinds are 150/300 and I raise to 1,200.

Button is the only caller.(stack approx 5,000)

Flop K-7-8

Not a great flop for me but I fire out 1,200.

Button calls.

Turn 9

I check and button checks behind me

River 10

We both check.

He has 66, and makes a straight.

Firstly why would you call with 66 against an early position raise of that size?

Secondly why would you call with three overcards on board with your only hopes a set, which could already be insufficient or a backdoor straight draw? The only thing he could beat was a stone cold bluff or a lower pp. Mystifying play that I can`t get my head round at all.