Yup. That's part of it. There can be many things that might kill overhead power lines. Trees overburdened by Snow/Ice. The lines themselves could have had weak points that caused them to break.
Unlike northern states that regularly see snow and ice that puts stresses on the lines, it doesn't happen nearly as often, if ever here. This can cause more failures in a situation like this, as marginal lines are stressed beyond their failure load. In places where these winter conditions are prevalent during much of the winter, those marginal lines would have probably failed piecemeal. Here, we're seeing all of the system abnormally stressed at once. In such a situation, you're going to see what are effectively multi years worth of accumulated potential failures happen all at once.
Add in solar/wind failures, difficulties in transporting fuel for conventional plants, and you're going to have pretty major issues. Rolling and hard blackouts should pretty much be expected.
At least we don't have annual rolling blackouts like they do in other parts of the country.
Talked to a Electric Generating guy years back.
What is the best fuel/system to generating electricity?
First, hydro-electric > Niagra Falls
Second, Coal. You dump coal beside the generating plant. Need moar power, feed in more coal. Need less power, feed in less coal. Zero delivery issues in a cold snap.
Natural Gas, Oil both also good when you want to ramp up power. BUT, you need a pipeline of fixed diameter and storage is more expensive than coal.