I have seen small bits of what seems like copper inside some of the holes, which seemed to me to also contribute to the effect of the bubbles, but not sure how they were made. The wax pellets makes sense.
They have been called lava beads by the Czechs, but they obviously are not lava.
On the market, most beads that are actual lava are brown or black (sometimes coated in a wax). However, in the last five to ten years or so, I have also seen another material being sold as lava, but it is entirely manmade. It comes in a variety of colors. It is a little bit heavier than the actual lava beads, and the texture is more consistent.