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.
You can understand how desperate Manchester United were to score a goal by looking at the statistics below.
Manchester united outplayed Arsenal, the statistics is there. But Arsenal did a great job in the defend, they park the bus and did greatly, the pressure was much on their defenders, the Manchester united attackers were too fast in the attacking line, and if they keep playing like this, they will end in the top four. The only mistake the Amorim made was not to start Benjamin Sesko in this game.
As manchester united fans, i wash really excited with the performance, but we wanted more. we were just unlucky in this game, and Arsenal used their foul set piece to score the only goal. It was a foul on the keeper, but Var did not check it. Premier league official can do better, such foul should not be ignored.