The second link says:

"each utility is required to lower the demand on its system based on its percentage of the historic ERCOT peak demand.

"each utility is responsible for determining how to implement the required demand reduction, most utilities use rotating outages for this purpose."

There's about 25 different utilities, so who knows what each does.

I'm surprised voltage reduction isn't used. It's very effective at reducing resistive loads (ie: heaters and incandescent lights).