Are you sure it would have been written in Greek. John was Hebrew. Why do you say Greek (just asking not questioning)?
John was Jewish, but Greek was the lingua franca back then and the common language of Judaea at the time was Aramaic. Take note of where the apostles went when they left Judaea; their commission was to bring the gospel to the known world and to the lost tribes of Israel. Also take note of Isaiah 28:11.
Lest anyone say that there is aught special about the Hebrew language, also note that it was God that created all the diverse languages at the Tower of Babel as noted in Genesis 11:7-9.