Medication, behavior therapy, and growth over time can radically change scores for a child with ADHD. The particulars of the scores (subtests) already acquired may be revealing of discrepancies.
If the parent feels these scores are inaccurate or incomplete, were I in their shoes I'd likely seek further testing to tease out details, in order to get a real sense of the child's functioning. From what you've said, I'd likely rely on a private tester for more information, rather than a school tester.
My aim in testing further would not be to sift for "gifted" scores, but to get a sense of what the strengths and challenges are at this moment in time, so I'd know what to work with and how.
