A little boy in flannel pajama pants and an orange shirt is playing the guitar on the couch.
The boy wants to be a professional guitar player when he grows up
A boy is playing guitar doesn't necessarily imply he wants to be a professional guitar player when he grows up.
A little boy can play a guitar and not want to be a professional guitar player.
A boy playing guitar does not imply that he wants to be a professional guitar player when he grows up.