Beach goer's sometimes take their jewellery off and lay it down on a towel, usually covered up so it doesn't get stolen while they play frisbee, build sand castles with the kid's, go into the water to body, surf board etc; . Their kid or even they themselves quickly grab the towel to dry off and the chain, ring etc; gets buried or partially buried and then maybe gets stepped on or a beach chair is moved and bury's it further out of sight. They may even forget about their jewellery until after leaving the beach and it's very hard to find a ring without a detector on a stretch of beach. Many years ago, I remember observing a guy using a rake to methodically rake a strip of beach trying to find a ring he had lost. He was a surfer and had placed the ring under a towel on a rock and it had flew off his towel into the sand. I was on vacation and did not have a detector at the time to help with a retrieval.
I know all these scenarios happen because of the first hand stories I have personally heard and I'm sure you all have too. People generally are relaxed and carefree at the beach and so they forget to take care of their personal stuff so it's not too hard to find treasure! but a chain like what was found here is a bit of a rarity considering it's size! but they do get lost in the sand at beach's all around the world!