It is clear that teams like AC Milan Roma and even Como are taking their games seriously which is good sign for building confidence. However as you noted these results do not guarantee success in league. Biggest surprise is Napoli poor performance but with new coach  Antonio Conte it is more likely that they were focused on getting team fit and ready for season other than winning. Real test for Napoli will come when league starts as coach Conte knows that preseason results are less important than being prepared for long season ahead.