What you guessed but according to the statistics the result of the match should have been in favor of Manchester United but Arsenal played badly but won the match. I don't know which statistics you are talking about in favor of Arsenal I see that Manchester United won only 2 out of 18 matches in the previous seasons in the Premier League and I thought they would win the match. They started the match very well but in just 13 minutes one of Arsenal's defenders Riccardo Calafiori scored but it was a great goal but no Manchester United forward could succeed in scoring the goal in the rest of the match.
In this particular fixture the statistics doesn't really matter because both teams are very familiar with each other due to their constant meetings almost every season but due to the decline of Manchester United it became very clear that Arsenal had the advantage to win considering their level of consistency in the league finishing 2nd place severally, though the home side played very well but failed to find the back of the net after conceding a goal in the first half.