This sort of thinking is endemic in industrial networks; they finally internalized basic ipv4 concepts in the late 00s and never considered maybe the stateful tracking required for UPNP and other NAT tricks also might exist without it.

I've set up several private v6 networks to deal with renewable energy projects in which the integrator used the same ipv4 address blocks on every single one, and the whole 6to4 translation explanation landed like they had just seen a devil sorcerer graft a goat head onto a human.