Now wait a minute here! Are they inferring that Jesus never cracked the Bible? Are these people inferring that nobody ever taught Jesus? No. "Not having learned" means that He was not taught in their schools—their rabbinical schools. Jesus' teaching came directly from the Father.
"Never having learned"? No. It does not mean that Jesus never learned. It means that He did not go to the same school, the same rabbinical schools, that they did.
Oh, He was taught! He had the greatest and best teacher. He had the greatest and best and most important education anybody on earth in all of the history of mankind ever had, and it was already showing when He was twelve and one-half years old. No, He was not taught by men. He was taught by the Father. He did not need to be taught by men. He had the best teacher that there ever was.
So "not having learned" means that He was not taught at the rabbinical schools the way the other religious leaders were. He was not taught by men. He was taught by His Father.