Hm. I read "grossly inappropriate" as modifying "other behavior," rather than "violence, harm, or other behavior," but I guess that could be an unintended construction.
I'm pretty sure it was an unintended construction. If it is not, very few parents could ever attest to that their child "never demonstrated or threatened violence, harm, or other behavior that is grossly inappropriate toward any other person." For example, if "grossly inappropriate" does not modify "demonstrated or threatened harm," most parents could not sign the form because most kids have at some point hit a parent in frustration and/or said "I'm so mad I'm going to hit you." That's how I view it anyway!
But of course if you are worried that your answer is not honest, I would certainly add any explanations you feel necessary concerning that yes/no question. (Put a star by your answer and say "see attached.")