Those islands were claimed by Japan in the 19th century. Japan annexed them along with Okinawa in 1879. And China did not say a thing about it. Then 16 years later after the Firse Sino-Japanese War, China formally turned them over, along with Taiwan.
This is where China's interest in these islands formally ends. Well over 100 years ago when they themselves turned them over to Japan after loosing a war. Then you try to nitpick 50 years later, when Taiwan was returned to Chinese control. Fine, China got Taiwan back, but these islands were not in the treaty that returned Taiwan to China.
So as I said, to China a treaty does not matter, because they are trying to reclaim lost territory over 100 years after they lost them. And this predates the treaty between the US and Spain after the Spanish-American War. So it is very relevant. To you the only reality that matters is what you think matters, nothing else.
This is why you consistantly fail, over and over and over again. You get back a large island, then proceed to loose that and whine for the next 50+ years about that as well. To people like you, every bit of land that China eer owned appears to rightfully belong to China, and should be returned. About the only immediate neighbor that China has not had to fight since the founding of the PRC is North Korea. And I bet if they were not so convienent as an antagonist against the US they would have been invaded as well.