Visited yesterday without charging.
The charger is in the parking lot designated "Parkieren nur gestattet während Aufenthalf im Restaurant", but I suspect that sign pre-dates the charger and it makes more sense if the charger is open to everyone.
In the evpass app, the location is just called "Elektrizitätsversorgung Berikon EVB" with free parking and no restrictions, without any mention to the restaurant. The roaming name on IchTankeStrom is "Berikon Restaurant Stalden N2".
It's only one of 2 chargers operated by Elektrizitätsversorgung Berikon, it would be strange if it was exclusively for clients of the restaurant.
There's a contactless reader built into the charger so it was probably available at some point, but it's not offered on the screen. There are QR codes for ad-hoc payment.