He probably broke them. Non-displaced fractures are missed on more than 50% of XRays, even dedicated "rib films". Regardless, the treatment is the exact same. You cannot splint ribs, it's just pain control and making sure he breathes deeply. "Splinting" is the body's reaction to chest wall pain, meaning you take shallow breaths. Forcing him to take deep breaths (through pain medication and an incentive spirometer) is the best way to prevent pneumonia.
To tell you the truth, in my practice, if a patient has rib pain after appropriate trauma, they get the diagnosis of a rib fracture even if I dont see one on XRay. We miss them so frequently that you need to assume it is broken even with a normal XRay.
There are only 2 ways to find out. A bone scan, which is a waste of money, or an XRay in about 1-2 weeks if he is still having pain. If you see a callus, then he had a fracture.
Regardless, he's gonna be out awhile, and I expect a DL stint. Even if he didnt break it, he's gonna hurt for a week plus, meaning he's probably DL bound