Reading online, there is a significant number of people who believe Jesus was a Christian.
To my mind that would require Jesus to travel to the future and read the new testament. Then go back in time to follow his own teachings and fulfil the events of the book.
Is that what happened?
According to Catholicism, was Jesus a time traveller?
The simple answer is no.
Jesus Christ, the Second Person of the Blessed Trinity, in his human nature was truly Our Redeemer and brought us out of sin and into a life of sanctifying grace by his death on the Cross for our salvation.
There are no Catholic teachings that state Our Lord, while in his human nature was even remotely considered a time traveller, moving back and forth in time!
There nothing to imply that he was anything in his life that could compare to Doctor Who and his *or Black Adder with his time machine (Back & Forth).
Many Christians believe that Jesus is Christian is simply due to the Fact that Jesus was the Christ and died on the Cross for our salvation. Thus Jesus is to be considered the founder of all Christendom.
In fact the Followers of the Way were first called Christians and is even mentioned in Scriptures as such. The word Christian is used three times in the New Testament: Acts 11:26, Acts 26:28, and 1 Peter 4:16.
And when he (Barnabas) had found him (Saul or Paul of Tarsus), he brought him to Antioch. So it was that for a whole year they assembled with the church and taught a great many people. And the disciples were first called Christians in Antioch. - (Acts 11:26)
Then Agrippa said unto Paul, Almost thou persuadest me to be a Christian. - (Acts 26:28)
Yet if any man suffer as a Christian, let him not be ashamed; but let him glorify God on this behalf. - (1 Peter 4:16)
If we considered Jesus to be the foundation of Christendom, I guess that would make him a Christian, but not a time traveller.
To my mind that would require Jesus to travel to the future and read the new testament.
To your mind, yes; but, then again, you're not Einstein. The world-renowned physicist taught that the space-time continuum is relativistic, to the point to which a hypothetical observer, situated outside of the Universe, would witness all events happening simultaneously. (This scientific idea is usually, and somewhat incorrectly, rendered into lay terms as time being an illusion, of sorts).
Now, Einstein was clearly Jewish, and it is to the Jews that God, which certainly meets the above-mentioned criteria of an objective observer, revealed both Testaments. And this supreme God was likened by the famous philosopher Socrates to a Mind, whose Thought or Reason (Logos) orders the entire Universe. Since Logos also means Word, this idea was later picked up by both Hellenized Jews (Philo of Alexandria) and Christians (John the Evangelist), due to its similarity with the first chapter of the Book of Genesis, where God, through words, orders the Universe into existence.
This Mind, then, along with the Thought indwelling it, witnesses all things happening simultaneously. As such, to the extent to which Christ was truly the embodiment of the divine Logos (Logic), time travel was not needed for Him to know or read the New Testament, despite it being written decades after His time on earth.
Christian was a name given in Antioch to the followers of Jesus Christ and His teachings (Acts 11:26). Is not a name self-imposed.
Jesus is God (John 1:1,14), and He live a perfect life without sins (1 Peter 2:22). Jesus never transgressed God's commandments (His commandments), so in that sense it could be said that He was a jew but also a Christian. There is no need to go to sci-fi to find an explanation.
