What Byrne knew about gyms was that they were places to train. He knew little about the specifics of Pokemon, and while he was sure gyms were mentioned in their context, he figured it was the same thing as the gyms he knew: where people exercised and trained. So when this kid said he was a "gym leader," Byrne highly doubted it. He looked too weak.

"I doubt you're a gym leader," he said flatly, "Whatever that even is."

He never bothered to actually study Pokemon or any of the other species here. It never interested him. He figured a "gym leader" was one who owned a gym, who trained the hardest and earned the rights to leading it. Well, Byrne was sort of right. He just didn't know that it applied to Pokemon.