They're going to need coordinates (unless they want to search the whole arena) in order to remove the chest.
It's arena 4. If you stand at the spawn with the beacon as north, I'm pretty sure it would be NW. I can get exact coords in an hour or so when I get home.
It's not a bug. I downloaded the map to record and explore. Basically they way sg maps are made is a large map is created and built for the arena. All hidden chests are added to this area (sg 4 will be a good example) before the dome is. In some cases chests will be placed too far out.
As you can see here, the land and everything is pre-made and chests pre-placed. When the map is completed, the dome is world-edited in. I mean sure, the chest probably gets items like every other chest, but it's no big deal.
How this is a bug I don't know The world was obviously generated before the glass was added (the spherical boundary), The chest is.... well.... its just there