Yes, slow playing a set if rarely a good play. But ......

..... let's be clear, there's never any 'nevers' in poker, nor are there any 'always'. (and all you smart asses out that all know that I don't mean garbage counter examples like AA always wins at showdown against KK when the board is 39J27 where neither player has a flush ).

In this hand, the opponent (read as: victim of bad suckage) didn't really slow-play his or her set. And the hero (read as: player who was obviously very confused about this hand), didn't exploit that opponent's play.