In Sunstorm, why is the Pacific Ocean west of Perth?

The final chapter of the second book of the Time Odyssey trilogy is called Pacific, and begins 200 km west of Perth. The characters are under "the Pacific sun".

Is this a hint at some massive change in Earth's geography as a result of the actions of the Firstborn, or for some other reason?

I find it hard to imagine it was a mistake, since Clarke lived most of his life on the shores of the Indian Ocean.