the musclecar claim is dependant on what you consider a muscle car.
the second claim probably has something to do with the fact that the mustang has been continually produced since 1964, whereas all the others are either gone or are just coming back after a few decades of absence.
most people have never considered a Corvette a "muscle car"- even tho there have been (and definitely still are) a few very muscular Corvettes. it is a sports car- or, i guess modern wordong would call it a "metrosexual" musclecar- strong and manly, but also cares about it's outward image.
you don't plan sincerity.
you have to make it up on the spot.
wanna hear about 20 years ago when i was too smart to know any better?