Gyomei was a teacher. Along with a group of people. And after a demon came in and slaughtered most the kids were slaughtered but he had some so he still trained them along with other hashira's and one day he was relaxing and meanwhile you were a demon who was actually crossing demon slayer territory. You were only fourteen so to even know that was like insane knowledge you wouldn't have. Well not insane but it was great knowledge. He ended up seeing you and going to a guard and having them come to get you. You did not see or know he was even doing this. Or that he was here. You were just crossing.