Are there any other reasons for congestion in newborns besides reflux? oh, in the absence of cold symptoms.

Yes: Silent aspiration, where the baby, when nippling, has a poor or abnormal swallow and the formula or breastmilk goes down the trachea (windpipe). Also, if there is a heart problem, the first signs can be failure which can present as congestion.

Could be more...: I would agree with the physician above and add if the infant placed a foreign body in their nasal passageway, and as simple as it sounds, sometime they just get a big booger that obstructs over half their nasal passage diameter causing them to be congested.