This should not come as a surprise. It's not uncommon for Texas DCs to do this in the Summer to reduce load on the grid during very hot days. They are often notified a few days in advance and compensated for it beyond fuel cost and equipment wear & tear. With all the hubbub lately, they knew this was coming.
It serves 2 purposes: A, a data center can basically be paid to run on generators, and B, they can control when and how gracefully they transfer load (can give generators the opportunity to warm up, a luxury they seldom have) because they may end up losing utility at some point regardless.
- Matt