“No wonder he was a Catholic”
Augustine lived from 354 to 430 AD.
The Great Schism occurred in 1054
The Reformation occurred 1517 – 1648
His options were somewhat limited.
Luther, Calvin and Zwingli all drew upon Augustine so they might not have seen your point.
Yes, Augustine was not Newman, but the "acorn" analogy was what Newman could use to justify the extrapolation necessary for his specious Development of Doctrine