I may be totally off here, so take it for what it's worth, but when I read your post it triggered a memory of something the gifted screening team said regarding my son. One of the reasons they didn't want to recommend testing is because he did not show initiative to extrapolate upon the problems given to him during the screening session. They informed me that one of the traits of giftedness is "expanding upon problems, showing creativity in moving beyond what was presented".
I named off numerous examples of his creativity and initiative to extrapolate on things that inspired him, but he was what I described as a "effort efficient worker".
They eventually capitulated and tested him, and he was high gifted in all three exceptionalities. His unwillingness to expand beyond the assignments for which he sees no purpose beyond busywork is still a part of his learning style, but I don't much care now. He's not a performing monkey there to impress the teachers; he's in school to gain skills and knowledge for his own future.
Perhaps the teacher is under the misguided idea that every gifted kid always goes beyond the assignment on the page every time they have an assignment.
Just a thought. I might be totally off, but I did find many of the teachers who were not actually trained in teaching gifted kids had some very limited, often biased ideas of what "all" gifted kids should be like.
