It says "there are three that bear record," it does not say "Trinity," or "Godhead." Such attributed titles are found in sources outside of the Bible. However, they are supported by Biblical quotes and evidence. Such sources are letter of the apostles, letters and preachings of those who were apprenticed to the apostles, various early church sermons, etc. As I said, when you do research of the earliest Christians, the results point to Catholic Doctrines, such as the Trinity, the hypo static nature of Christ, and so forth.
The trinity is not a Catholic doctrine, it is a biblical doctrine. Jesus said, "I and my Father are one" John 10:30.
The word "Catholic" does not appear in the New Testament.