In this case, if you dropped the note in the right place, there is a 'line with no tags of any kind.  I think streetcomplete may take this as potentially a road.  In some places I see intermittent streams with no tunnel/bridge/otherwise designation.  That may also cause this to trigger the bridge quests as well.  As for here, the line with no tags, I think its a boundary but looks like a big can of worms to open and clean-up.