I would assume it's someone's belief as to how something is linked to their referred or already diagnosed conditions. Assuming you're active duty utilizing IDES, you won't have to worry about primary or secondary terminology unless you intend to file again for more benefit in the future.
Here's how the process has shaken out for me, as I don't know where you're at in the process, what branch you're in, if you're active or not, and what elections you've made:
Active USMC utilizing IDES. At the time of board, all diagnosed conditions were: back pain, adjustment disorder w/anxiety & depression symptoms.
I made a claim list much longer than that, I believe 24 claimed conditions were inputted (though more likely broken down to 19, things like mid-back pain & lumbar pain would get conglomerated into a DDD diagnosis).
The examiners from VES issued diagnoses for most of my claimed conditions, only referring one and outright rejecting two. I claimed the conditions, I was examined, I was diagnosed, and per the decision letter/notification letter I was shown all diagnoses made were service connected. Whether there are secondary considerations is largely inconsequential. As I said before there are a myriad of secondary conditions that can be claimed should there be an intent to file in the future.
