The thing is, there are two types of muscle physiques: lean and bulky. A lean physique is described as having small and thin, but firmly-sculpted, muscles. A bulky physique is described as having larger and wider muscles. Girls want lean physiques, not bulky physiques, so doing more reps with lower resistance tones your muscles for that lean physique.
That's just the hair, and are you sure it isn't just a digitally-modified picture?