I may be wrong, but I suspect that it's not neon at all. Those look like flexible linear LED luminaires to me. With proper cold cathode kit, and a proper old-school bit of highly-skilled tube bending, they could have done much smoother curves and far sharper corners. Unfortunately it would also have been incredibly fragile (a similar project in Edinburgh has had to be removed because it's already been smashed twice) so that's another reason to use the LED kit - they can take a bit more of a bash.
Still, a fun little installation!