What is non stimulant response impulsivity?

Are you asking if. Impulsivity, a symptom of adhd responds to non-stimulant medications, like atomoxetine or long-acting guanfacine? Each child's response is different, but there's ~ 65% chance these will work. Stimulants (methylphenidate & amphetamine) work 80-90% of the time for symptoms of both inattention & hyperactivity/impulsivity. Long-acting Guanfacine can be given with a stimulant, also.
I can try to guess. As often times, stimulants are used to treat the impulsivity associated with adhd, for a child who continued to display impulsivity while receiving stimulants- I might see how that could be referred to in the way as phrased in your question. I am not sure I find it to be a particularly helpful description for a specific subset of patients. If you heard the doctor say it, I would ask about it.