Porto and Leipzig were the visiting teams who successfully beat their opponents but that was because their opponents were not as strong as them. Atletico Madrid almost got good results like Porto and Leipzig but Lazio's enthusiasm and their goalkeeper managed to score a goal in the final minutes of the match which was extraordinary because it saved Lazio from defeat at home game.
Newcastle realized that playing more openly would make their defense easier for AC Milan to penetrate, but in fact, Newcastle did not apply a defensive strategy because they placed 3 attackers in front, only that it was difficult for them to counterattack because AC Milan played very pressingly and quite dominated the match. When they played at home, Newcastle opened up the opportunity to win so they are a team that other teams in the group have to take into account.
Specially for Leipzig they were vastly better and I can see why they ended up with a win, it would have been a shocker if they lost that game. Obviously we are talking about something that is a bit beyond what it could be a problem too, but at this rate I believe that we are going to be doing fine and Leipzig will have a chance to stay at second position until the group is over.
Milan vs Newcastle was the talk of the town and everyone wondered who will win that game, and it was a tie as expected since everyone knew that they were too close in talent level and that's how it ended. When people do not know which one will win, unless one side gets lucky, a tie is not a shocking result and could be the most common result.