I think this match was a bit really about luck with the way I watched the match. Manchester United also did well in their performance; they did not perform poorly as we were thinking before the start of the match, although I know they were ready because they know how strong Arsenal is, and that is why they came ready to play the match.
However, this is the time Arsenal needs this win the most, and they failed to win this match, which is very bad for them. They should be the ones to at least record this 1 goal; it would have been better for them, but Arsenal failed to win the match. Although, as you said, the possession of the match was with Arsenal, but not luck to win.
If you watch Arsenal's game against Manchester United, I doubt you'll consider it lucky that Manchester United was able to draw with Arsenal at home. Manchester United's performance against Arsenal was worth the draw, in fact, they deserved to win because they surpassed our expectations. I expected Man United to concede two goals to Arsenal, but it was clear that Arsenal was lucky to draw, if not for Raya, they would have conceded a goal in the final minutes of the game.
Even though Arsenal scored the opening goal, it will not help them win the Premier League or make Liverpool feel uncomfortable about winning the league this season. Liverpool presently has 70 points, 15 ahead of Arsenal. At this point, Arsenal have to work hard to keep their spot among the top four, and this is the third season in a row that Arsenal has finished third in the Premier League.