The equinox occurs in a few hours. In the northern half of the world, it is spring, and the start of a year has been linked to it in many times and places throughout history. With fairly good but not decisive meteorological justification, it is considered in some place, at least the US, the start of spring. I have talked about all these things before.
The fact that Google has decided it is one of the many events marked on it's search pages is unremarkable. The fact that it has translated it onto the Australian search page as the start of autumn is straightforward but slightly naive, since it fits awkwardly with our pretty strong tradition of starting seasons at the start of the month. But what in the world does The Very Hungry Caterpillar and the fruit it eats have to do with the "start of autumn"?