This is not the first match in which Dortmund has acted in this way against a strong opponent, they did something similar in the match against Newcastle. For Dortmund, an away draw is a completely acceptable result, but for Bayer it is a loss of very important points, now Bayern will almost certainly be able to take advantage of these and get ahead of them, although if they win they will be equal on points, but Bayern will have a better goal difference.
If we talk about the theoretical situation, Bayer still have an advantage - firstly, for Bayern to catch up with them, they still have to win the game in hand. Secondly, even if Bayern wins, the teams will have an equal number of points, but the remaining head-to-head game will be on Bayer's field where they can tip the scales in their favor. But these are theoretical considerations, it is clear that Bayern actually remains a very big favorite.
I wish Leverkusen would have won the game as this draw is kind of annoying for both of them. Dortmund couldn't get any closer to the top and to Bayern and Leverkusen couldn't turn their dominant game into important three points. No need to discuss that a win would have been preferable for obvious reasons, but it is true that Leverkusen has the game against Bayern on their home ground. To tie a game against Dortmund is ok and Bayern will have some weaker games, too. But we can already see what's needed to stay level with Bayern. Wins, wins, wins.