The fixme says "Area is approximate - details to be clarified". It's a bit of a stretch to get from that to the area being "... land which was previously developed which is not currently in use. Brownfield land may be vacant or scheduled for future development."

The way you edited is actually part of a correctlt tagged landuse=residential multipolygon, https://www.openstreetmap.org/relation/12286304

I've reverted your edit.

You can read the documentation on landuse=residential and landuse=brownfield here:
https://wiki.openstreetmap.org/wiki/Tag:landuse%3Dresidential
https://wiki.openstreetmap.org/wiki/Tag:landuse%3Dbrownfield