I say he is 50-50 to cap the turn with QJ.

A) 3 bets on 4th street and 3 on 5th is greater than 4 on 4th and 1 on 5th if he believes thats how the hand will play out. In terms of a deception layer he knows that you think QJ WOULD cap the turn, therefore in game your likely to hold that read and raise on the river.

B) He doesnt like variance and is waiting for a safe river card to start pumping his hand again.

I actually much prefer the call on the turn with the nuts.