Very interesting! While my lvl 30 character didn't quite find the greatest loot in it, but as said, some very helpful stuff, great find.
I wonder now if there aren't more of these hidden around, as a little trick the developers used to test/demo characters, hidden chests to give almost the entire variety of items...there is at least one type of any of the items in the game in that chest. I would bet there are more of these inside/right outside of towns.
Just tried it out and it is legit. Noticed the stuff in it was the exact same items that the Khajiit merchant right outside of Dawnstar was selling. To test it, I emptied out the chest and then went back to the Khajiit merchant and sold my legendary Daedric sword. Went back to chest and lo and behold it was in there.