Maybe he got into the car and was going to cheat on his wife/gf, and instead of having consensual sex, he ended up being held at gunpoint.
That's the only decent explanation I can think of, because getting into the car to begin with doesn't seem innocent. He wanted something. Nobody just gets into the car to show them directions.
And yeah, he may have felt aroused during the whole thing, but that doesn't mean he liked it, so it's a crime. Joke all you want, but I wouldn't want it to happen to me at gunpoint. It'd be different if it was a hot teacher who seduced me as a student, where I do have a choice (although I am young...), but if it's done by gunpoint, it's not really fun, and it's not your choice anymore.