There were two very similar posts on CV - this and the one it (almost) duplicates (at least, if you count the Q in comments, it's a duplicate). I marked the linked one as a duplicate and was in the process of answering the other, but some computer problems delayed my answer, which was then migrated (and my in-progress answer was lost in the migration, but I have since made a rough version of it in the migrated one).
The closed one clearly is on topic here, since it's a question about properties of forecasting time series.
Either one of two situations exist:
The one I linked above really is a duplicate, in which case the thing it duplicates must also be on topic and so should never have been migrated
It isn't a duplicate, in which case it should be reopened.
I believe the first applies (that the question in comments in the original post made it on topic, and at the same time made the second one a duplicate); however, picking either (1) or (2) is reasonable.
In respect of the post I linked above, as it stands currently the post it was closed as a duplicate of isn't a post on CV, so on what grounds is it a duplicate? It can only be a duplicate of the other one if the other one is brought back here.
It's possible it's a duplicate of another post, of course, but as it stands, something is wrong.