okay so see the pic its photoshopped so I could get both tooltips in the shot.

essentially I have been to this location and got the skyshard inside. however the zone guide doesn't count this. I assume there are some weird missing logs or some such. This isnt the first time I have noticed this strangeness but, it is the first time I have proof. take it as you will just being diligent. maybe help devs identify another way to track visited zones before the zone guide system was in place.
if the skyshard was activated you have def been in that delve/dungeon/etc