Don't know if that is true or not. A lot of things were handed down very accurately through oral tradition. Until just 160 years ago, reading and writing were actually a profession. One guy is a baker, another guy is a carpenter or a stone mason and someone else reads and writes.
In ancient times, writing was expensive, especially writing on parchment. It's not like it is today. If we make an error, we wad up the paper and start over. But if that single sheet of paper cost you $50, you are going to be extra careful and you are going to plan out just exactly what you need to say because you have limited space. Parchment was expensive to make and so you had to get it right the first time. Hence, you hired someone to write it for you as you dictate the words.
Writing was prohibitive expensive and precluded each person having their own personal copy of the Scriptures, which we take for granted today. So oral tradition made sense. That is how they taught the Scriptures to their children.
When you consider how long Paul's letter to the Romans is, it had to be a very expensive scroll. Since Paul's and the other apostles letters had to travel to and fro across the expanse of the Roman Empire, they had to be written on something durable like parchment, not papyrus.
Paul would have been one of those who were blessed with literacy, but he still likely employed others to write for him due to his possible issues with eye sickness.