The stadium is indeed often called BORUSSIA-PARK. But technically, the football fields located next to the stadium and the biergarten also belong to BORUSSIA-PARK. You can contact the official club page for confirmation. The stadium itself, which is part of BORUSSIA-PARK, is officially named “Stadion im BORUSSIA-PARK”. The stadium tag only includes the stadium area, not the entire BORUSSIA-PARK area. I’ve made a tag which includes the BORUSSIA-PARK, which is technically a sports complex.
Here you can find some reliable sources:
I hope this will clear things up.
