Yes, that's right! This is the beginning of the new ecclesiastical calendar. We start the cycle of feast and fasts September 1st. And how? The first of the twelve major feasts days is the Nativity (Birth)of the Theotokos.
September 1st isn't her real birthday. But it's not like she is 8 and has to celebrate her birth on the exact day. It's more of an honor that the celebration of Christ's incarnation and resurrection begins with her birth because it was her obedience that brought the Light into the world.
So, Happy New Year!