According to the story it was at a sub station, which is transformers, switches and monitoring and control equipment.
A power plant is where power is generated.
There’s quite a story here. Luma taking over was controversial with the local left, and the 20 unions involved have threatened to walk out if the deal goes through. They were approved a year ago, and were supposed to engage in a planning process, culminating in taking direct operation this year. While it’s called privatization, almost all the funding is coming from the US government. Transformer fire could be their ratty old gear, or unhappy union types. A recent article quoted discussions about a large maintenance backlog.
At the moment, their web site is running DOS protection, which indicates they have tech chops and good reactions, could be a positive sign. Don’t envy anyone trying to operate a legit company in that environment of long term corruption, though.