$5 says welding accident during repairs or upgrades. Set off a load of fuel and there she goes. It did say injured "sailors and civilians" were being handled so yeah, probably civilian contractors doing an upgrade fucked up.

Same thing on a submarine a few years ago too. It happens. USS Miami a few years ago, a shipyard worker who wanted to go home set beds on fire with oil soaked rags, hoping a small fire would cancel his work. He ended up causing $600 million in damage. This could be a similar situation.