Since it was "midway" in the tournament, stacks were almost certainly not that deep, and then KK is just never a fold preflop. If the guy was making an oversized open shove like say 30BB, I will even discount AA a lot, since most players will understand, that they are missing out on value by playing AA like this. Instead I will expect him to have a middling pocket pair or a hand like AK/AQ most of the time, and then calling with KK is literally printing money.
And even if he has AA, it does not matter at all. If he had made a normal open to say 2,5BB, then you would have 3-bet, he would have 4-bet jammed, you would have called, and the result would have been just the same. Unless stacks are insanely deep, AA vs. KK is just one of the most boring coolers in poker, and the guy with KK always goes broke. Unless of course he manage to crack the aces