larger demand for power (due to cold) can cause an outage.
The cold could build up snow and ice on the lines causing them to be a lot more heavy in the weather and break (and add in wind effects)
to say nothing of animals or trees falling.
Then you have humans ending up doing stupid things in an attempt to stay warm and stay alive.
There are lots of things that can cause power outages. Why it is so in this case, I don't know myself.