or maybe he was holding the necklace in his emotional state because he assumed Jin kicked the crap out of him because he found out about him and Sun. Then someone-maybe Sun, doubt it, but maybe, or more likely someone else sent by Sun's father because he figured Jin wouldn't go through with it then pushed him over.
In the end, it was basically just a way for Jin to see the necklace and discover that Sun was cheating on him, going to te line from Sun to Sayid that Jin knows she betrayed him.