ADHD is sometimes used as a catchall to mean a set of behaviors that does not coincide with the majority at school or work. Ive met a bunch of people on ADHD medicine, but it was usually because they wanted to force themselves to be good at or like something they didnt want to do normally.

In this case its called ADHD because the student has found their own way to solve it despite the method the teacher is teaching and that the rest of the class uses.