Dortmund are at the top of the standings at the moment not after beating Bayern Munich, but this was obtained by Dortmund after Dortmund were able to beat Frankfurt at their own turf with a large score without any reply from Frankfurt. It was this victory that brought Dortmund to the top of the standings because at the same time Bayern Munich was defeated by Mainz so that Dortmund made it to the top of the standings after being able to win a lot over Frankfurt.
It was a fantastic victory for Dortmund after beating Frankfurt 4-0 without reply. This victory was very special because Dortmund managed to shift Bayern Munich's position at the top of the standings for the time being. But indeed Frankfurt's defeat seemed excessive, Frankfurt should have also scored a goal in this match to cure his sadness even though in the end they still lost. Currently Frankfurt is in 9th place in the standings, they are still quite safe, but if they keep losing next week then Gladbach's chances to shorten the gap will be even more open.
Dortmund victory against Frankfurt was very impressive with massive numbers of goals, if Dortmund can continue with a great performance like this winning Bundesliga won't be hard for them , with addition of Bayern Munich poor performance, Dortmund will grab this opportunity.
Dortmund were able to secure a remarkable victory with Frankfurt. Dortmund managed to top the points table as Bayern Munich lost a match. But I think Dortmund won't stay at the top for long, as Bayern Munich will hope to win the next matches to take themselves more points to the top of the table.