I think this is a pretty straightforward play. Down to the final 3? The villain has to be on a wide range of hands, but let's analyze. He is most likely pushing AK, AQ, down to small pocket pairs at this stage. Since he didn't do that, we will assume he has a marginal hand. At 3 handed it could be virtually anything. Gigabet's holding is relatively meaningless here. So thinking about the play backwards and from the villain's point of view, he got trapped. Busted flush draw maybe? A-J or lower that just isn't callable to an all in bet. I may be underanalyzing this play, but nothing shocking really stands out.