Fulgarites are formed by an unspecified heat source. As the electricity disperses to earth the heat diminishes. This makes for big variations between fulgarites formed at the point of impact to areas fused by dispersed heat/energy.
I have found pieces which are both solid and with interior channels. The surface of pieces which have been buried in the desert for some time and eroded look a lot like the beads on the strands pictured.
I have posted a couple of other pics of pieces i have found in the Sahara. The fresher pieces look different to the eroded ones.
I suspect that wear, or indeed 'preparation' of fulgarites for decorative use would lead to an appearance such as that in the beads shown.