Before we get too excited, note how far out to sea that zone goes. It's not like the Chinese were sailing in under the Golden Gate.
Stay calm. Beijing isn't going anywhere. We can always nuke it later, if we feel the need. Which I'm hoping we won't, because come on. There are people there. Nuking cities is a bad thing to do. Let's not rush into things like that.
Attu Island at the end of the archipelago is closer to the coast of Russia than Anchorage: way closer. Those things go way out into the Western Pacific. Still, this could be a test. I wouldn't get too concerned about this. We need to stop feasting on fear porn.
Nations don't build huge military arsenals, not to use them in some manner. Any Chinese territory near the Aleutian Islands? Then it's obvious why their warships were there.