Is there a separate guest block in the BVB stadium?

Just the same reason as the south blocks are separated from each other:

After the official complaint of a family father, who, due to the partially densely crowded spectators on the southern tribune, saw the integrity of his children endangered, the District Government Arnsberg insisted that additional open spaces be set up in the standing area of the southern tribune to increase safety. This measure is intended to keep rescue routes free, which, in case of emergency, provide the medical personnel with quick access to the site of the accident. allow for rapid evacuation of the entire grandstand if required.

Source: Wikipedia

In order to be able to effectively keep these free areas free, there are among other things fences.