橋のデッキと通行可能なエリアは必ず同じではない。ここは https://wiki.openstreetmap.org/wiki/JA:地物ひとつにOSM要素はひとつ の原則に従った。https://www.openstreetmap.org/way/850416757 に`bridge=yes`を補足すればok。
個人的に見ると `highway=footway` + `area=yes` を `highway=pedestrian` + `area=yes`（iDプリセット名"pedestrian area"）と間違えるのはより深刻な問題です。歩道橋で、作業・緊急車両通行可能な歩行者専用道路ではない

The usage area is not always the same as the bridge area. This has followed the principle of One Object, One Feature. Only `bridge=yes` should be added to https://www.openstreetmap.org/way/850416757 . 
I'm more concerned about confusing `highway=footway` + `area=yes` with `highway=pedestrian` + `area=yes` , because of iD's "pedestrian area" preset name. Service or emergencies vehicles aren't able to pass through such a "pedestrian street" footbridge. 