I've noticed that a lot of people mistake the review text-box with the one where they can ask questions, and end up submitting their opinion as a question.
I think that most of the people who mistake it just write in the first text-box they see, without reading what it says, that's why I think the text-box to ask questions on should be modified. Here's some ideas on how it could be changed:
A button that says something like "Ask a question", and after pressing it the text-box could appear.
A smaller button that shows an interrogation sign, next to a text reading something along the lines of "Ask a question", and after pressing the button the text-box could appear.
Making the review and question text-boxes look different, easily differentiate them, by changing the style of the question text-box (colour, shape, ...)