That's right, if Leipzig can maintain their good performance, it is very possible that they will make it difficult for Bayern Munchen in the future. Now Leipzig is one of two clubs that are still undefeated, their strength will certainly be taken into account by all Bundesliga contestants. It is possible that Leipzig will compete tightly for the trophy with Bayern Munchen and Leverkusen until the end of the season, although personally I hope Dortmund can also join in the competition.
So far, Leipzig can stay in the top 2 with the same points as Bayern Munich. Yes, they are still undefeated, they only got 2 draws. The point gaps between the top 6 teams are not very massive, I think those top 6 teams still have the chance to win the trophy. Which team can play more consistently, they will have more chance to win the trophy. Regarding Dortmund, they may have the chance to join the race of the title again if they can keep winning in the next few matches.
On the other hand, it seems that Leipzig is not able to show the same performance in the Champions League, they have lost to Atletico Madrid and Juventus before.
We can't compare the performance in Bundesliga and UCL. In UCL, the match is more difficult because the participants are strong teams in each top league in Europe. If Leipzig got a defeat, it is not something very surprising.