Swimming and broad shoulders

Hi, I'm new. :) It's often said swimming makes your shoulders broader. Does they come from a bigger upper body bone structure or due to prominent deltoid muscles? For me it's hard to believe that swimming in the developing age can make bone bigger. Are there any real swimmers who got broader shoulder from swimming after the developing age? I'm 23 years old with narrow shoulder and I'd like to know if swimming can help me. Thanks!