The question is located in the title. I apologize for prior confusion.
I have an extinct xenophobic culture that had made it to fusion and space-age technology. (Reason for xenophobism already thought of) I'll say the tech level in the beginning of Kim Stanley Robinson's Blue Mars.
Their civilization first developed on the Seychelles, Mauritia, and Mascarene Microcontinents, presently located about 1000 kilometers east of Madagascar and 100 meters below. The civilization reached this level by about 14,567 years ago, when an abrupt rise in sea level brought about its end. I can help with maps, such as this and this. All I have left is this speculation on the flora and fauna, and a technology timeline.
I hope these resources are sufficient.
Question: How could a technological civilization have arisen earlier?