Magnolia tree transplant
Leaf and flower buds that open in spring are set during the previous growing season. I would be surprised if the buds that you noticed this fall actually only started forming this late, but because they obviously start out small, it's entirely possible that they were not as noticeable earlier in the year.
The buds of many tree species are small and easily overlooked, while others, including magnolia, are conspicuous. I remember the first time I planted and grew magnolias, being very surprised by the size of the buds in the fall. In subsequent years I made a concerted effort to observe the bud situation of the trees, and they really do start setting the buds during the growing season after the tree blooms, but of course with the buds starting out small, they really were easy to miss.