A cylinder produces some amount of force per power stroke.
4 cylinders producing 10N per power stroke are not going to generate more "torque" than 2 cylinders producing 20N per power stroke, except insomuch as we're talking about vibrational losses, since there is an advantage to smoother power delivery with less energy being expended throwing the crank around.
In practice, however, a 2L V8 is not going to "make more torque" than a 2L I4 or 2L V6.
e.g., my car's 5.0L makes 80 ft*lbs/L at peak, while a 2.4L I4 out of a Subaru makes ~76ft*lbs/L at peak, and teh 1L I4 out of a ZX10R makes ~84ft*lbs/L
So now that we've eliminated that, why does it have a V8?
My guess is because they're unable to build an I4 that can survive at 15krpm like Japan can. More cylinders does make for a smoother engine without complex harmonic dampening, which the Japanese have decades of experience in doing exceptional at.