What did you think is https://www.openstreetmap.org/way/447222032 then?

From your wiki-link...
"A building passage is a tunnel that goes through a building, but is not inside the building itself (see pictured examples). The walls at both sides (and the top) of the tunnel are considered outer walls of the building, which can have entrances that lead into it. "

Thats exactly what it is, a (outdoor!) footpath from "Peiner Straße" to the parking at the rear of the building.