John was not wrong. Jesus was never wrong. He was talking about the seed of Abraham that other passages show went through Isaac to Jacob. It did not pass to Ishmael or Esau. Why is it important ? The Islamic religion traces their line through Ishmael. They hold Abraham to be prophet, Ishmael his son to be a prophet, and Mohammed the descendant of Ishmael to be "the Prophet." Details, details.
so just write Abraham out of the story. Good thinking.