They are Kind scenery, so will show in the Scenery tab in Surveyor. There is no such thing as Kind terrain.
I think the reason the DLS web page describes them as "terrain features" is that the creator assigned them to category-class XFC (which is meant for rolling stock, intermodal) instead of perhaps the more logical VL (vehicle, land-based). Kind scenery cannot act like rolling stock in the game, even if the asset represents something that is used for intermodal transport in real life. "Terrain features" must be the DLS's default description when it is confused by conflicts between Kind and category-class.
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