Do devout Catholics believe that God did not create death?

As part of the funeral Mass I attended today, the priest said that death was not part of God’s original plan but was caused by our sins. It’s not an idea I had heard before and I wonder whether it is doctrine. If so, what was His plan for all the people that would stay alive? Is it our fault then if we die? And how do we know what His plans were? Not meaning to be disrespectful of anyone, but the idea kind of took me aback.