The fence and remaining walking trail infrastructure mark the northern boundary where the Yaberoo Budjara Heritage Trail departs the Neerabup National Park and enters “no mans” land before eventually entering the Yanchep National Park.
I was wondering that as well, my only answer: The road coming in from the left is the official Elbe cycling-way "R1" and just descended from a bridge over the Mulde river, the cycling-way continues as a fully asphalt-road on the right side all the way through the forest. The road entering on the right was a local road for farming and forest-ranger vehicles. It's a dirt road continuing on the left side into the forest.
Fun fact: About a mile and a half into the forest, the paths cross again, cyling-way continuing left, forest track going further on the right hand side.
I guess it's just an example of German bureaucracy when it comes to building things. The R1 cycling-way has been built sometimes in the 1990's I guess and that dirt road was most likely there much longer, in order to avoid any bureaucracy obstacles they might've went for those crossings.