Looking at Key:industrial - OpenStreetMap Wiki, the page says the tag requires one of:
I.e. the same tag should be used for different things? E.g. industrial=grinding_mill can be used on a landuse=industrial to express that this land is used with (one or more) grinding mills, or it could be used with man_made=works to express that there is a specific facility which is grinding?
On the other hand, the Tag:industrial=grinding_mill - OpenStreetMap Wiki page says the tag can only be used together with landuse=industrial, so it never would be a feature tag?
Maybe in this specific example, the wiki is simply wrong (and I just fixed it), because taginfo doesn’t even list a combination with landuse for the 34k uses of the tag: industrial=grinding_mill | Tags | OpenStreetMap Taginfo but it seems a general problem with the “industrial” tag and the suggested combination with landuse or man_made.