Calling/bluffing missed flushdraws have become a meme at this point. People point it out and can either say it's a good/bad call or a good/bad bluff
But here board is very dynamic, and lots of hands are close in equity on flop/turn:
1) OOP has lots of hands that want to x/r and see no more cards, folding out a bunch of equity. In particular his made hands (K6 on flop, 7x on turn).
2) IP has high regret betting with a lot of hands because of 1)
3) High diamonds give away the least equity in terms of free cards for IP, and are easy to play so tend to be the strongest part of check call range OOP (he also x/c 2 pair on flop sometimes). Also IP is barreling super aggressively due to high OOP x/r, so high diamond cards have v good capture factor with very clean outs when hit.
4) On river OOP has a high number of diamond floats which has to fold (100% freq ignoring preflop- JTdd, QTdd, K8dd). He also has some pair hands but these are mostly neutral in suits.
5) Because OOP diamond floats HAVE to fold, IP does not want to bluff diamonds (othersuits relatively neutral). Meaning pairs made with diamonds become v good unblocking bluffs. Again, SB is not bluffing diamonds.