Bill Tindall, E.Tn.
The 8 mortises are cut and tenons fit to them. As you can see all 8 of these M&T joints need to line up exactly or this thing won't come together. It did, thankfully. I'll describe the glue up puzzle later.
The arcs on the vertical post elements were band sawed. Many would then fair the arc with a disk sander or with a spoke shave. I find a hand plane works dandy. As seen in PIC 3 the band saw tooth marks are used to gauge shaving removal to result in a flat surface.