Wikipedia says ‘Short ribs are a cut of beef taken from the brisket, chuck, plate, or rib areas of beef cattle. They consist of a short portion of the rib bone, which is overlain by meat which varies in thickness.’
Browning meat, also known as searing does a lot for a dish: it locks in and deepens flavour (and moisture?) as well as adds colour to the finished dish. It might also kill bacteria that may be on the surface of the meat.
Anyhow, the surface of the meat caramelises in what’s known as the Maillard reaction. The flavours that develop are a combination of nutty, caramel with a hint of bitter.