Its reasonable to interact with another human and expect that they are roughly similar to you, especially when your interactions match what you'd expect.
That doesn't extend as well to other species, let along non-living things that are entirely different from us. They could seem intelligent from the outside but internally function like a lookup table. They also could externally seem like a lookup table while internally matching much better what wed consider intelligence. We don't have context of first hand experience that applies and we don't know what's going on inside the black box.
With all that said, I'm phrasing this way more certain than I mean to. I wouldn't claim to know whether a box is intelligent or not, I'm just trying to point out how hard or impossible it would be today without knowing more about the box.