If google maps told you a main road was closed, would your first instinct be to suspect that google maps is lying to you for the first time since you started using it? I'd sooner suspect a meteor landed on the road.
Especially as Thursday (the day this happened) is a public holiday in Germany, where bigger projects that require a complete closing of the highway (e.g. demolition of an old bridge) are often done to impact traffic as little as possible.
i don't use Google Maps for guidance. Google Maps was never built to do this. It was added as a "feature", but still does not work well, for the data it collects.