Did Cardinal Schonborn write the Catechism, and can it contain errors?

You take both as true. It is a fact that Cardinal Schonborn wrote the 1992 Catechism, because John Paul II gave him that job. They used Schonborn's catechism, which was given an imprimatur by Cardinal Ratzinger, for the official Latin 1997 Catechism, which John Paul II said came to us by his Apostolic Constitution Fidei Depositum, because it had an imprimatur on it. But an imprimatur does not mean it has no mistakes; it can very well have them, and many people have found many mistakes in the Catechism. If the pope had said the Catechism is infallible, then we would say there are no mistakes in it, but he never did. The pope said it was a valid and legitimate instrument and a sure norm for teaching the faith, not that it was infallible in every word. Something can be valid, legitimate, and a norm without being infallible or perfect. The word infallible is never used in connection with any catechism, not even the Tridentine catechism. Canon 749 says that unless it is manifestly evident that a teaching is infallible, it is not; so we would need someone with infallible authority to declare the Catechism infallible, and they do not, because they know errors are found in it every so often. A faithful Catholic can read the Catechism knowing that by and large it is good, but there is a small percentage where people have found real problems, and sometimes it is not heresy but something not said properly, as when it treats Muslims believing in the same God we do and moves on without qualification. Part of the problem is Schonborn's own background: he is a liberal, and you can see subtle messages of his theology throughout the Catechism.