It has been my experience that people don't normally call with 2-6 offsuit (or any other hand that didnt hit here) unless they are going to attempt to bluff you. so he either had a draw of some sort or believes his Ace high might be good. this knowledge leads me to the belief he has some sort of hand here most of the time. if he was on a straight draw, he hit it; if he was on a flush draw, he hit it; if he had a pair, he already hit it. i dont think he is folding to a 1000 chip bet, when he will still be in decent position to get ITM.