God is the first cause of everything, therefore he’s the first cause of every event.
However, eth is probably referring to God’s plan. He authored it. It included the fall.
However, the author of a book is not liable for the acts that the characters in the book commit. They commit their own acts IF they are free. And these characters were free.
Calvinists believe that humans have free will. They just think that they’ll always without fail use that free will unwisely.
That is in stark contrast to much of what has been said on this thread.