I see that the value is also available in the iD editor, and you may want to consult that editor for more information. Based on what I've seen elsewhere, it also most likely resembles the main picture here: https://wiki.openstreetmap.org/wiki/Tag:bicycle_parking=wall_loops

Though the picture in the wiki shows that the anchor is not attached to a wall, which may be why it was labeled as an anchor instead of a "wall" loop. The "wall" part of the name may be confusing to some people. It could also be interpreted as a generic anchor that is likely a type of wheelbender where only 1 wheel can be attached.