I agree, it is not very clear, but it seems to me it is relevant that nowhere do they say you are required/must inform USCIS of divorce proceedings, but they do explicitly point that out for other information. They also say they will ask for a waiver request in the RFE, so they seem you assume that you did not request a waiver, for whatever that is worth.
Since it is not clear, in my opinion it is good to check with a lawyer. And if not sure, get a second opinion from a second lawyer... (Sorry for repeating myself, but that is a very important point in my opinion.)
Regarding the case that boiler and MikeE reference, that case seems to have more going on than just a divorce. Didn't read the whole thread, it was looong, but he did adjust from a tourist visa (so basically proof of misrepresentation already), and his info in N-400 and i-751 did not match. Red flags all over the place for that guy.