A telling situation

A recent trip to the casino and I entered a simple $60 buy-in tournament, which usually draws about 150 or so entrants.
My opening table was a relatively conservative group. The kid two seats to my right looked like he just turned 18, but he showed to be a decent player. He showed a nice amount of aggression early without playing wild and he built up a nice chip stack.
I'm moderately ahead of the table average, but behind this kid when this early-stage hand comes along with me in the small blind.
I'm dealt AQ off suit. Action gets to him and he raises to 300 (blinds are 50/100). I call and one other player stays.
Flop is 8K5. I am curious as to where I am and bet moderately 300 and stare straight ahead. But because I am in a corner type seat, I can see the kid out of the corner of my eye. Other guy folds and the kid sits there staring at the board. After a few moments pass and me staring straight ahead he calls.
Turn card was another low card. I check and continue to glaze forward. Again, he stares at the board, looks down at his chips and bets $500. I call.
River is empty 8, pairing the board but not helping my hand. I check again and get the same reaction from the kid. Looking at the board, nothing more. I look at him. He stares at the board, then looks directly down at his chips, grabbing about $1600 which he throws in the pot.
I'm dead. I have nothing and he's been betting the whole time. A call makes no sense for me because if I do it and lose, I'm down to about 600 chips.
I still question his hands: Does he have quad eights? Does he have trip eights? Does he have a king?
To answer I replay the hand in my head, and quickly eliminate an 8, mainly because a flop with a king probably would have slowed him down a bit. The couple hands I've seen him show down his style has been limp with small to medium pairs and raise with Ace/anything, and I haven't seen him show down high pairs.
I don't get into all the reasoning here, but eventually I figure his likely hands are AK or pocket kings. But as I replay the hand, the most important factor stares at me: he never looked at me, or my stack...and this has not been in his style except very early when we were all even.
His actions were look at the board and look at his own stack, moves some very inexperienced players will make when they are simply asking themselves, how much can I lose if my bluff fails here. (People that watch tell videos or study tells know that if a player looks at their chips it's usually a sign of strength. But this tell is almost always done immediately and often without thinking, a big difference from what he was doing). If he had trips or even a king, he'd be more curious to find out how much more he can win from me. And so his bet seemed more random than "I really want you to bet."
And as I try to decide my move, I look at him, look at the board, look ahead and pick up my cards, shuffling them in my hands. He can't take his eyes off the board.
I call. He turns over A 10 off, and I take down the pot. From that point forward, I pretty much own him the rest of the tournament, and the table also sits shocked I made the call. But it made it a lot easier to build up my stack from then on out and leave the table many rounds later as the large stack.

As a side note: The kid outlasted me. He got a few nice wins on races and kept playing an overall solid game. He and I ended up at the same table together when I got eliminated outside about 6 spots outside the money. My losing hand was AK, which fell to pocket jacks.