Of course it's placebo, that's the point. What else could it be, some substance in the car? The point is that self-perception can influence brain chemistry and hormone production.
To be picky: it also doesn't provide responsiveness (i.e. agility), but in isolation tends to muscle boundness. Easy to address with other exercise of course.
Well, maybe, and that needs to be ruled out. Plasticizer vapors, such as those present in newer cars, have been said to mimic human hormones before.