A musician playing his violin.
The violinist is on stage with other musicians.
Not every musician playing a violin is a violinist . just because a musician is playing his violin doe snot mean that he is on stage, or that he is playing with other musicians.
The first sentence only speaks on the actions of the subject and not that he is playing on stage nor that he is playing with other musicians.
The musician could have been at home and not on a stage with other musicians.