Dortmund almost became German champions last year and only some sort of curse prevented them from beating Bayern. So Dortmund is a very strong team that can play on equal footing with the strongest groups, which is proved by the fact that from the group with PSG, Newcastle and Milan they went to 1/8 Champions League.
They should have won the match with PSV, but the referee awarded an extremely controversial penalty, which should not have been awarded, because the Dortmund player played into the ball, not into the feet of the PSV player and because of the referee's mistake Dortmund lost 3 points.
Dortmund is not a strong challenger and they always fail to be the best even though the hope to get success is in sight. The Dortmund group phase managed to escape but I am not sure they can go further because their appearance is sometimes less consistent. Moreover, the Champions League is very competitive and very different from the domestic league, so the competition here will be far more difficult than in the domestic league.
A draw at home to PSV Eindhoven is indeed very beneficial for Dortmund because in the second leg they can pursue goals at home. If you look at the opportunity in the match Dortmund should be able to score more than one goal but not put to good use. PSV Eindhoven managed to master the game and dominated the match better than Dortmund but unfortunately unable to add goals.