Arteta did what a proactive manager would have done, they saw an opportunity and they took it. If Arsenal had dropped points today, Arteta would have been questioned for his competency in leading Arsenal to winning the trophy this season. Liverpool is not a team that's dropping points lately since they dropped points yesterday Arsenal needed to capitalize on it and I am impressed that they did just that.
If you look at Arsenal over the past few seasons, including last season, you probably wouldn't have been overly critical of Arsenal's victory at Newcastle. When talking about the competence of a manager like Arteta, that should have been discussed a few seasons ago, or even before Liverpool won the Premier League last season. It's no secret that Arsenal can be good at the start of a season, but towards the end, they start to lose consistency in winning matches, a situation that has happened to Arsenal repeatedly under Arteta.