If you live here in the Philippines and hear every petty aggressive move by China it builds up. Still, lighting up a Japanese destroyer with targeting radar is edgy stuff.
Remember the way WW1 got rolling, it was unstoppable after a small indecent. The animosity between these nations may not be fully realized by you guys. China hates Japan for WW2, and Japan just elected a guy who is preparing for war. I think in certain places it's seen as inevitable. During a still difficult time in the Mideast the US is sending ships here at a pretty good clip so someone thinks its possible.
I don't think this war would be as bad as if the Cold War turned hot, the Chinese just don't have the nukes in qty, it would be suicide. The destruction would not be mutually assured. I believe it would be conventional. China is seen as possibly having an ace up its sleeve with its ballistic anti ship missile. That may be their ticket to an upset win, and that would change the world. If the Chinese government believes it can win that's all it takes. If they think the US won't support the Philippines they can start the ball rolling. The US cannot let an attack slide. If the US turns a blind eye to an attack on a Philippine garrison in the EEZ then can Germany, UK and France trust our word?
Consider Argentina with its invasion of the Falkland Islands. Who cares, right? Yet p r i d e got the Brits moving. The Argentine government was a dictatorship and they used the invasion to garner support, keep their heads attached to their necks. China might be doing the same thing. Internal decent might be the driver here.