Even labeling the two small islands in question Senkoku, the Japanese version, instead of Diaoyu, the name in Chinese, is controversial, almost like picking a fight.
What's in a name?
Sometimes identity and the pride that goes with that.
Thus, although the islands China asserted sovereignty over this week in the South Pacific by sailing "surveillance ships" near, do have a nice oil and gas field, that's not really the main point of this dispute.
The main point of this ongoing dispute is the long-running Sno-Japanese argument about who's the Big Dog of East Asia, Chow or Akita?
Although the Chinese are normally cautious using force, as opposed to saying "We will allow every city to burn to the ground that the River Yangste to turn red all the way to Chongqing rather than let you do X," given other tensions in the international system, namely Iran, one would want to be pretty wary of having this independent dispute escalate.
That's how the Chinese signal things linguistically, by making statements of the form, "You can kill all those Chinse, but we won't back down."
Now since the Chinse "surveillance ships" went back home rather quickly, and unlike the last time didn't collide with anybody, presumably the point has been made that the Chow is a Big Dog in East Asia not to be trifled with, even by an Akita allied to an American Pit Bull.
It is a reminder of the benefit that would accrue to all parties in the international system were there arbitration of words, not arms, over certain territorial disputes in East Asia that would make both Japan, China, and Korea less reliant on Middle Eastern oil so subject to religiously motivated risks not easily predicted in terms of timing or emotive response, if pride makes doing such a thing difficult.