See the screen.get page. It has this sentence for the screenitemids parameter:

Return only screen that contain the given screen items.

While initially it might seem that only one screen would be returned in this case, the type here includes array - that indicates that multiple screens can be returned. If that is correct, "screen" should be changed to plural.

In any case, it would be great to clarify how the screenitemids parameter works - does it return screen that contains all of the passed IDs, or all the screens that contain any of the passed IDs?