The people who got shafted during that ice storm had signed up with a thing called griddy which was selling electricity at wholesale in exchange for a subscription fee. Unlike most customers with fixed rates, griddy customers had variable rates based on the wholesale spot price at the time of usage.

My car radio used to be inundated with ads for griddy subscriptions. I'm pretty sure they went away entirely after February 2021.

Two points on this:

I haven't followed up, but initially the Texas state government pretty much ruled fuck the consumers who got caught up in this. Don't know how that ultimately played out.
None of what I've just written absolves Texas of their shitty grid management. I went to bed on Tuesday night during that storm with an in house temperature of 28 degrees, quietly resigned to the possibility that I might not wake up. I didn't have water for two weeks after the pipes burst because plumbing parts were in such short supply and those that were available were jacked up many hundreds of percent in price.

To this day, any freezing weather frightens me. Fuck Texas and everything about it.

But those statements of enormous electric bills are slightly overstated and spun for narrative quite a bit.