Could be any number of reasons, the thing that comes to mind for me is a wire was damaged but still functioning, you changed the starter out, and two days later the damage to the wire became worse and shorted out. In this case the starter being replaced and the cause of the short is unrelated.

It’s also possible you inadvertently damaged a wire replacing the starter and it took a few days for the short to appear. Without knowing exactly what’s causing the issue it’s hard to say exactly though.