The trivial proof of the GP's statement is that there are regions of the world and the US that regularly drop below 20F and have a functioning electrical grid (say, for instance, Alaska).
That's not proof at all. Building grid infrastructure that can function below 20F in regions that reach that temperature regularly is easier in important ways - in particular, if a new piece of infrastructure gets built that can't cope, the problem will happen early on and either get fixed or worked around, whereas somewhere like Texas can build up decades of new infrastructure that can't cope with the cold before anything happens to demonstrate that.