After a suggestion that EL wire might be to blame, it appears as though that is the case.

EL wire fits the colour of the digits (since they are obviously not a 'neon' orange/red, but more a yellow/orange). EL wire can be cut and joined (with care) and could be done in a way to form the sharp corners (eg: middle of 3, top of 1).

Still a guess that plexiglass is used to hold the digit wire in place... the shading/translucence of the 'tubes' around the circumference would hide the apparent presence of plexiglass sheets. It would also explain how all the digits (between each 'tube') appear the same as the ones beside it.

Even if they aren't real nixies., the size of the thing makes it pretty cool though! The build has obviously been done with care.