It’s not possible to second guess the treatment choices made by a surgeon 10 years ago. There’s a lot of unknowns in the case. Most often, if someone breaks the bones near the elbow and dislocates the elbow as well, surgery is done. The surgery is meant to stabilize the elbow and ensure that there’s no further damage from the fracture.
However, there are situations where this may not be needed. Perhaps the fracture wasn’t near the elbow itself, but further up or down on the arm? Maybe the surgeon felt that the elbow was quite stable after it was put back into place? At this point, we can only guess at what the reasoning was.