I’m not saying that there is only support for AfD in east and none in the west, but there is definitely more support in the east: see recent state elections map.

A ton of AfD support is actually geographically split. Much of the support is in former East Germany, not in the west of the country. While their overall support has been rising steadily, this could have been a bellwether moment that showed that support rising to electoral success in the west. These results aren’t a mystery, they’re just not a simple as you would believe reading only headlines.