villain either has a set, an overpair to the flop, or a flush

if I felt that villain has a set I would lead, for value and also so he doesn't catch a flush if he has a diamond in his hand

if I thought villain had an overpair on the flop, the ace of diamonds is not a card he wanted to see, and would make him more inclined to fold when pressured- however, I would still bet here if you think he had overs on the flop, since your actions up to this point indicate to the villain that you're likely not on the flush

if he has the flush you want to check and try to see the river cheaply
however, given the preflop action, the only hands villain could be holding here is KdQd, KdJd, QdJd, or 10dJd

weighing all this, I think it makes it correct for gabe to lead here on the turn- I think he's giving up value and making it harder for himself by checking and giving up the initiative