Liverpool beating Arsenal doesn't mean anything in the grand scheme of things for the short term, because lets be honest Liverpool will lose a game too, it's possible for them to go unbeaten but I doubt it, they will lose, and Arsenal can cover that difference.
That assumes Arsenal will win whenever Liverpool loses. I think last season or the season before that shows that Arsenal struggle to close the gap when it matters.
It is indeed a long league, and even the best-prepared teams can sometimes make mistakes. But Liverpool's victory at least gave them maximum points and put them in a better position to close the gap. We all know how unpredictable the EPL can be. Smaller teams can change the course of the league. They can beat the big teams and vice versa. So, the best strategy is to always get 3 points in every league game. Because the league is decided by many games and all of them are important.