Side eye is a bizarre thing to complain about. Drill sergeants say it (at least in movies) if a recruit looks at them from the side, rather than stare 100% straight ahead.
Therefore, “side eye” equals looking at someone who is talking to you. I am aware of no court rule or even social norm that would prevent a witness from looking at the judge.
I’ve never heard of such a complaint and that’s why I believe the judge was acting crazy.
Such a wacko judge could just as likely complain that the witness *wasn’t* looking at him.