I've talked about this here before, and idk if I'm normal or not, but I have a physiological response to extreme fear that's very much like arousal. "Vagina tingles," wetness and all. It doesn't happen often, but on the few occasions I have been genuinely scared for my life, it did. So it's not at all hard for me to believe women experience arousal during rape (an orgasm I have more trouble understanding, but having never been sexually assaulted I can't really rule out that it would happen.)

I imagine it has to do with blood flow and adrenaline making your body mimic the signs of arousal. The situations I experienced it in weren't sexual scenarios at all (one time a dog attacked me, another time I almost drowned,) so I know it had nothing to do with being severely turned on or anything. It was purely physiological.

Having an underwhelming ONS is a pretty far cry from being in a physically dangerous/life-threatening situation, so it's not surprising that the latter might cause women to experience these symptoms while the former doesn't. Those are two thusly l totally different situations and the body reacts in different ways.