Both. They sent me a Letter of Inquiry explaining. At the start of the letter it listed two sections of concerns, the first being all of the items on my credit report (not just the omitted ones), and the second is 'conduct', which includes not listing all the debts, and a disciplinary action I had at a job in '15.
I have to write back with 4 pieces of information - 1, the circumstances behind each item on my credit report and what I plan to do about them, 2, documents and proof supporting the first section, 3, explanations of why the items were omitted, and 4, the reason for my disciplinary action.