The collapse process is reasonably clear – the bottom casting broke at the lower attachment point
If the F20C rudders are attached in a similar fashion to the old N20, then another possibility is that the castings had vertical play/slop in them. When this happens its possible for the top eyebolt to come off the gudgeon and then torque the bottom casting on the pin. The new pins are double welded and pretty robust so it wouldn't surprise me that it could break the casting instead of the gudgeon like they used to.
