AQ facing a bet on KK7 flop

[Steamboy]

This is a hand from an 215$ aussie millions sat at partypoker
no read on opponent.
Party Poker No-Limit Hold'em Tourney, Big Blind is t1200 (8 handed) internettexasholdem.com

SB (t7996)
BB (t37122)
UTG (t22730)
UTG+1 (t18656)
Hero (t41132)
MP2 (t23997)
CO (t42007)
Button (t15839)

Preflop: Hero is MP1 with Q[img]/images/graemlins/diamond.gif[/img], A[img]/images/graemlins/club.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">UTG+1 raises to t2400</font>, <font color="#CC3333">Hero raises to t6000</font>, <font color="#666666">5 folds</font>, UTG+1 calls t3600.

Flop: (t12000) 7[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG+1 bets t7200</font>, Hero folds.

Final Pot: t19200
I think that the size of the bet after the flop in relation to his stack(5406 left after the bet) is a sign of strength. Why doesnt he go allin. Am I right thinking he wont fold if I raise. But wouldnt he check if he had AK and made a set.
how would you play it?