The right answer for anything like this entirely depends on your class-- maybe your textbook, probably your lectures, and certainly your instructor. We can't tell you that. For example, it is unclear if your instructor wants you to do outside research (it's not hard to find articles or even full books about passives!) or just use your own observations-- from what you said, it's just your own observations, to that should not be especially difficult, nor should we help you with it.
It seems that the word choice of "remarkable" might have been unfortunately misleading. Think of it in the scientific sense: something that must be explained. Just try to describe the constructions in detail and compare them in those details. How do they differ, and how are they similar? That's what linguists do in general, but it should specifically answer this question.
Syntax is basically just detail-oriented pattern analysis while searching for generalizations-- both patterns within languages, and similarities across them.
If you aren't sure about the expectations, you must talk to your instructor. You won't find the answer online.
