The nuclear element is staying. We know Cranston’s character works in a nuclear plant so all signs point to this being the origin story of Godzilla though nuclear power is not the central theme.
That doesn't follow. In the Heisei series and a couple of the Millennium movies, Godzilla's mutation made him nuclear-powered and he needed to feed on nuclear reactors and high-energy sources, which is what drew him to civilization. Yet all those movies were sequels to the '54 original. So including a nuclear plant doesn't prove it's a rebooted origin story. It could be, but that particular piece of information isn't probative.