My Husband Has Noticed Bruising On Both Toenails (big Toe)

My husband has noticed bruising on both toenails (big toe) with no pain and no recollection of stubbing or dropping a heavy object on them. Could it just be as simple as subungual hematoma or could it be a symptom of an underlying medical condition ? He is not a diabetic, no circulation issues or high blood pressure that we are aware of.