Anemones can and will kill fish, and from your description of the clown's behavior, it is possible that's what happened.
If your friend bought an anemone to host his clown, he should have researched, certain anemones are not compatible at all with certain clowns, and certain anemones do better with certain clowns. In the end, there's no guarantee that the clown will favor an anemone in the first place, a lot of them just ignore them.
Besides the ones that Yote mentioned, tube anemones come to mind as another type of anemone that doesn't need strong light.