Lord Fiery was indeed a fire Elementalist, but he also had a hidden talent he never told others about.
Did he have magic? No, he didn't. Is he a descendant of the wizard? He wasn't either.
But he has an ability that no one has. He had a god-like eye that could see what no one else could.
From the start, Lord Fiery already knew Kazuto and Hiro had magic when the two of them first arrived at the academy and took the grade-level test. The lord also knew that Kazuto put on a magic restriction on his body.
At that time, Kazuto didn't know how to balance out his two contrast energy to make him fall ill whenever he used magic.
On the other hand, Lord Fiery never felt the flow of magic energy inside Richard and Niken. Nor could he see their deepest part of their astral dimension.