The statement you give in the OP title is both true and untrue.

The modern branded "Oktoberfest" is originally Munichian in it's origin, and was started originally in 1810 to celebrate the marraige of the Bavarian monarch, Ludiwig I of Bavaria to Therese of Saxe-Hildburghausen. The original celebration was a fair held from 12-16 October 1810. In modern times, the date of Oktoberfest has crept a bit earlier, and often starts in late September. Since 1991, efforts have been made to time the festival so that it extends over the weekend nearest October 3, which is German Reunification Day.

However, Oktoberfest and it's many imitators (domestic German and otherwise) draw from an earlier tradition of fall-time fairs and harvest festivals that probably dates back to pre-Christian antecedents. In fact, most European peasant cultures had some sort of harvest festival that fell during the months of October or November, and that's the time of year when many German towns would hold one of their annual fairs.