I believe the catgut may actually refer to catgut!

The 'bugles' referred to are, undoubtedly, 'bugle beads'. These would need to be attached in some way and catgut may have been the preferred method as it would be stronger than plain cotton thread.

When I do beading, I usually use a nylon thread (not unlike catgut in a violin string) because it does not fray like regular cotton thread does when chafed by a cut-glass bead.