Yes, a 4- or 5- yard kilt can be bespoke, even when made from PV or other materials. It is not synonymous with the term "tank". The term "tank" (which as I understand it, was coined on this forum) refers specifically to a kilt that it is made from 16-oz wool, 8 yards (or thereabouts), and hand-sewn. It should also have an internal stabilizer and interfacing, as well as other details which make it "built like a tank". These are usually bespoke, but I don't think they necessarily have to be in order to be considered tanks.

So while a kilt may be bespoke, it isn't necessarily a tank. And while a tank may be bespoke, it doesn't have to be in order to be a tank.