I mean the tag you added is redundant / duplicate information. It is already covered by the main key "man_made=milk_churn_stand". "subject" is for objects (memorial, artwork) which depict or commemorate something or someone.
https://wiki.openstreetmap.org/wiki/Key:subject:wikidata

If you intended to re-tag it as memorial, you should change the main key as described here;
https://wiki.openstreetmap.org/wiki/Tag:man%20made=milk%20churn%20stand?uselang=da#Memorials_in_the_shape_of_milk_churn_stands