What you're talking about here is not that. His play makes no sense, BUT that doesn't necessarily make it collusion, either. It's far more likely, imo, that for whatever reason you, specifically, were his target. Maybe you pissed him off earlier, maybe he didn't like your avatar, maybe he drew straws before match and picked you. Who knows? Anyway, it seems like he wanted you out regardless and was willing to let the other player live in order to achieve this goal.
While, mathmatically and financially, his play makes no sense; that doesn't automatically make it collusion either. He is free to play any hand in any manner he wishes. It only becomes collusion if he had a prior arrangement with the all-in player that he would fold to him at the end, rather than look him up. Or, some similar agreement, prior to this hand, that they would work co-operatively regardless if either of them became short. Something like that.
Bottom line is you can't collude with yourself. If he just let this guy live to get get you out because he had targeted you that's a douchy move for sure; but it's not evidence of collusion. To collude the other player would have to be actively working with him due to a prior arrangement where they would soft-play each other even if the math said not to.