The use of the phrase "aspect of your personal background or identity", inclusion of the sentence "Many applicants will not need to answer this question", and the list of examples they give made it really seem only focused on identity based/personal background diversity (aka not diversity rooted in unique traits, experiences, thoughts, etc.) Based on past threads I browsed, this was what other people interpreted it as too. I would say if you feel you could write a strong essay that conveys a unique part of your identity and background, go for it!
I didn't think my diversity essay or background was compelling enough so I went ahead and submitted. Its not like I'm even getting an II anyway so whatevaaa