I would say it is a genuine temporary box or a very clever way to make it look like one. The label has the distinct font type that can be found on genuine labels and documentation. For example look at this document to compare: https://www.thebigbigtrain.com/wp-content/uploads/2016/09/TBBT-service-sheet-48.jpg
Also the label is placed on the side of the box instead of the top. That could indicate that the box was stored in a store, stockroom or warehouse because then the label would be in a convienent place once the box was stored.
I also think it is possible that the product description is different. It simply did not fit on the label. Take a look at this post :The Big Big Train packaging variations and rare boxes
You will notice in the second picture that the bottom box has “BIG LOAD OPEN WAGON” printed on the side while the top box only shows “OPEN WAGON”
Anyway, just my two cents.