I think that really explains a tremendous amount about his frustration level in school and I think we'll be able to better advocate for him now.
Good for you! What a relief.  It is great that he has lots of gifted peers and programing, but some advocacy/tweeking of the regular program does seem to be in order.  Just think how much worse it might have been if you lived in a disctrict without any accomidations for gifted kids!
You refer to the program as HGT...What does the H stand for? What are the cut offs?  Is it a full day, 5 days a week program?  Have you called the school to schedule an appointment to review the test results?  Will you start with the teacher?
Best Wishes,
Grinity