It is not infrequent to have air escape from a lung in the setting of moderate to severe blunt chest trauma. Often (but not always) this is associated with broken ribs. Whether the rib fragments actually puncture the lung, or whether there was an acute, sudden intrathoracic pressure rise that blew OUT the lung, is something we could only know if we were actually able to see the inside of the chest. As the majority of blunt trauma patients don't undergo either thoracoscopy or thoracotomy, we really don't know why the air escaped from the lung in most cases.
What is important is not whether the lung was punctured, because lung heals quite well. What is important is the amount and type of the damage to the lung tissue. What you don't want to have as a diver is any part of the lung that is isolated behind a very narrow air passageway, because that's when expanding gas can't escape, and can lead to AGE. Extensive scarring can do this, which is why I mentioned ARDS (which results in scarred lungs). In the majority of simple, traumatic pneumothoraces, no major damage to the lung tissue was done, and the minor damage that allowed the air to escape will quickly heal. That situation should present no increased risk for diving at all.
This is in distinct contrast to SPONTANEOUS pneumothorax, which is where the lung had an area that was sufficiently weak that, under normal stresses, it ruptured. Lungs which have such lesions often have multiple weak areas, and are prone to recurrence of the problem (up to 50%, in some studies). Since recurrent pneumothorax is a potentially lethal problem if it occurs underwater, such patients are universally, as far as I know, advised not to continue to dive. But this is based on having abnormal lungs at baseline, which the trauma patient generally does not.
