Arsenal is still fine, but this loss does of course have some drawbacks as a draw would have been much better as it would have kept the distance between Arsenal and Newcastle. Now Newcastle is in the middle of the competition for the top ranks again and that raises pressure for all of the teams at the top. But until mid of December Arsenal will have a few games in the Premier League that won't be as hard as the one against Newcastle.
For Liverpool this draw was a disappointment I think. Since Aston Villa and Arsenal lost their games, Liverpool had a tempting chance to create some distance. Still not much, but some distance that could also snowball later on when the teams behind fail once more and Liverpool has a streak, this can quickly grow to 6 points, which is quite comfortable. But they missed that chance.
Although Arsenal has gone undefeated this season, Newcastle has broken Arsenal's records. Newcastle is playing to finish in the top 4 of the league in order to qualify for the next UCL. I think everyone knows that Arsenal is playing well this season, their loss to Newcastle was still unexpected, and all of their players are available. Although Arsenal missed out on winning the Premier League title last season, they are now finding it so difficult to be at the top.
Liverpool's draw against Luton Town is a big disappointment for the team, as Luton Town is attempting to avoid relegation once more. The Premier League has become difficult for Luton Town, as proven by their one win this season, which came at the 80 minutes of the match. Despite this, all Liverpool squads have performed well, and it is surprising that a team as strong as Liverpool cannot defeat a team ranked 17th in the league. Moh Salah was also unable to make a difference on the game, possibly because of Arsenal and Aston Villa losing their matches, which is why Liverpool is hoping to finish in fourth place. The game would have ended in a 1:0, if Diaz hadn't scored in 90th to draw the match.
I think the loss against Newcastle wasn't precisely unexpected, there was a realistic chance for Newcastle to win that game. It wasn't as if everybody thought they wouldn't have a chance. Though I did not expect that Arsenal wouldn't score and that one goal would be enough for Newcastle to get the win. I think Arteta reproached his whole team for not scoring a goal in that game. There wasn't enough thrustfulness in their game.