The FMC question would be a perfectly fine if it was prefixed with "Assuming a long over water leg with no navaids available..."
I think half of the battle with these exams is to decode the examiner-spiel, even if the question, as apparently it did in this case, emanate from a Boeing manual or wherever.
I think my old English Lit. Tutor (sadly now RIP) would describe the wording of such questions as "lacking intellectual rigor"