I have some experience with this.
The difference between a hairline fracture in the rib and a severe bruise in the rib are very difficult to diagnose. In the end doctors don't spend a lot of time, at least initially, trying to find the difference as the treatment is the same. Its not like an arm that you put into a splint and imobilize if there is a break but just wrap in an ace bandage and ice if there is a severe sprain. The ribs have to continue to move if you intend to keep breathing and hairline fractures in the ribs aren't cause for surgery. You basically just have to wait for the ribs to heal.
There have been some questions about the Red Sox medical staff in the past, most famously from failing to diagnose Curt Schilling's career ending arm injury when he was signed prior to the 2008 season. But I don't think this is cause to blame the Red Sox doctors.
FWIW Doctor Thomas Gill, the Red Sox physician is a very well respected doctor with sixteen years experience, and the chief of sports medicine at Massachusetts General Hospital, the number five ranked hospital in the country according to U.S. News and World Report. I'd certainly go see him or his staff if I were hurt.
Their affiliated hospital is the Beth Israel Deconess Hospital which is also a nationally recognized hospital and where I personally receive my care.
As I'm sure you all know, Boston is nationally renowned for its plethora of experienced doctors. Its a little silly given all this information to question if the Red Sox doctors know what they are doing.