What he's telling you is that the price of gold and its usefulness are implicitly connected. Yes, the price isn't directly related with it, it's a matter of supply and demand. But, if it wasn't useful, why would it be demanded? People evaluate goods by their utility. If they all had the properties of a store of value asset, they could also be used similarly by the belief that they will be used essentially in the future.

Gold does have these properties and is, thus, stored with the conviction that someone will use it to either create jewelry or experiment with it in chemistry, or use it into electronics etc.