There is only one restaurant named Atrium in this hotel building.

I surveyed it today and asked: they confirmed there is no such restaurant.

This Bruzz article seems to be the key: there is some confusion, because there is only Atrium here.
https://www.bruzz.be/en/culture/eat-drink/eneko-basque-brussels-intimate-dining-where-you-least-expect-it-2022-04-08

Closing.