Weinzierl's team twice came from behind to earn a 2-2 draw at Signal Iduna Park.
"I'm very happy, we were very strong mentally," he told Bundesliga.com.
"We said to ourselves at half time that anything was possible today, we just had to believe. We kept playing and eventually got our rewards."
The result meant that Dortmund have now failed to win in their last four home league games.