I was actually going to use that as a second example in a different form, namely that even if the person was a police officer, that fact is irrelevant if the officer didn't identify himself.

But let's look at something like that which is similar to the case here. Suppose a police officer did the above and I didn't stop and the police officer shot me. If I yelled out, "YOU SHOT ME!", would that be a defamatory statement because the officer had a legal right to shoot me?

It's the same thing here: if the passenger experienced something that a reasonable person would have viewed as a "rape", the fact that the action was legally authorized doesn't change her perception of it. Thus the SOP isn't legally relevant.