Stud8 - Is this Collusion?

[SCSTWG]

During the course of this hand when he makes the check raise on 5th street, you may have to consider that he has trip 4's and was waiting until it was a full bet to get max value. I actually like his raise in this spot because you showed weakness on 5th with your check and he is figuring if you checked you are not calling 2 bets. He then has a decent low draw and is probably in front for high. I don't see any collusion in this at all.