Thinking and taking information in at the same time, especially in gifted kids, is a very difficult combination. When a child (or person)is ideating for conversation, formulating their thoughts to comment, they will look away from the face of the other party because the face is so information rich it is distracting to the ideation processes.
Unfortunately, years ago some good soul, made notice that kids on the spectrum have difficulty making eye contact. The education professionals have latched on to that as something to focus on with kids with learning disabilities. All through the school day you will hear teachers telling kids to look at them when the kid is talking to them.
In actuality, when conversing, in American culture, it is polite to gaze on the face off-and-on, not constantly, when being spoken TO. It is common and acceptable, and in gifted and learning disabled kids necessary, to look away when being the SPEAKER rather than the listener.
So, tell the teacher to lay off and focus on whether or not he is comprehending or able to communicate his ideas.