I was surprised, when I read that as well, but the articles in Sueddeutsche and Spiegel both give areas were voter turnout seems to be higher and were it is lower - so Bavaria lower, but Munich higher.

Therefore, an area that is traditionally voting for CSU has a lower turn out and an area that is tradtionally voting SPD has a higher turnout.

that still might lead to a lower overall figure.

of course, all this is fantasy land...