What are these stones?
From the image, they look like jelly beans (or in Serbian, dželi bins) to me, based on the size, colour (including the slightly mottled pattern which tends to indicate better-quality jelly beans) and shine. The comment 'inside is a mystery' sounds to me like a clear reference to the fact that jelly beans often come in a variety of flavours, and it's not always easy to tell from the colour what the flavour will be.
The more general culinary term (although it's not a common one) for confectionery with a hard decorative outer shell is a dragée. The 'stones' in the video could be sugared almonds, although they look too small in my opinion, or something like coated raisins or other nuts.