I lived in Texas and we never got rolling blackouts for this. We didn't hear about it from family and friends in every major Texas city. Maybe this means 75% of the state by area rather than population? We just didn't drive because much of Texas isn't set up to clear roads and, more importantly, few of our drivers know how to deal with snow and so most get very unsafe to drive around.

The report your wikipedia article cites for 75% says this: "In the case of ERCOT, where rolling blackouts affected the largest number of customers (3.2 million), there were 3100 MW of responsive reserves available on the first day of the event, compared to a minimum requirement of 2300 MW." So an eighth or so of Texas' ~25 million population in 2011.