Visited yesterday and did a short charge with eCarUp app.
The coordinates on eCarUp are correct. The access is through the road on the north of the building. There aren't any "Privat" signs along the way. In fact, it's unclear which parking spaces belong to the business or the ice ring.
The only parking spaces with signs are the 4 with charging stations, where it says "Nur für Elektrofahrzeuge".
Nothing clearly says if it's public or private, but the QR code signs say beware of roaming tariffs outside eCarUp, that there is no separate parking fee, and to please vacante the space when done charging, so it seems to be open to the public. One of the parking spaces was occupied by an electric company car, and they have at least one other electric car that was parked further away.
The chargers are not in a logical order. It goes 2, 1, 3, 4.
Number 2 is indicated out of service on eCarUp, but there's no sign of an issue on location. I tried plugging in to see, the green light switched to blue, but it never showed connected in the eCarUp app, and it was impossible to start a charge on it. Maybe it's just a networking issue. I then tried charger 1 and had no issue.