If someone went to England and took the rocks from Stonehenge and carted them off to a museum overseas, that would surely be stealing?
I think it was true, on some level, at the time the bust of Nefertiti was taken in the 1920s. Supposedly, the Germans nominally followed some sort of legal process for removing the artifact -- though perhaps with less-than-full transparency.
Perhaps there are other reasons to claim that Egyptian artifacts were 'stolen.' But I'm trying to have a conversation about what those might be since the subject is not as obvious to me as others seem to think it is.
We see this happening now on a smaller scale with metal detecting and what happens with their finds.