Many LD shafts use splices in the LD shafts, which is why those shafts to many have become synonymous to low deflection, even though you can make an LD shaft without splices and make a splices shaft not low deflection. It's been done for quite a while and several makers have very different ways of doing it. Jacoby does a flat laminate shaft with a ton of laminations, OB has a interesting interlocking splice, Predator may be one of the earliest and well known makers of splices shafts, they do just straight forward pie splices. Tiger has a square center dowel in the shaft with 4 splices around that.
I'm a bit curious how you ended up good enough or knowledgeable enough to order a custom cue, but not have heard of splices shafts since they are pretty common now.