I didn't understand these repeated digs at Christianity as having been borrowed from the Stoics. For one, that all bad things are actually good is not a tenet of Christianity and is not in the Bible. Perhaps some Christians taught this, but you can find a person claiming Christ who teaches absolutely anything you can think of. Such is the nature of things that are popular.
I can only assume the author is referring to this section from Romans 8:28 (NIV) "And we know that in all things God works for the good of those who love him, who have been called according to his purpose."
If you fly through too quickly you could reach the Stoic claim, but there are a few key differences.
1. It says "God works for the good" in all things, but not that all those things are good in essence.
2. This is a promise only to those who love God, not automatically extended to all people or things.
Finally, I'll note that the entire Old Testament predates the Stoics, and is the foundation for Christian thinking about God's will and plan for the universe.