There must have been a goal kick at some point which was an own goal.
This can't happen.
The ball must leave the 18 yard box to be in play. It's a corner if it is kicked directly into goal by keeper.
So it can happen then? Surely can leave box and go back in. Think I've seen it, some sort of crazy winds.
If by 'it can happen then' you mean the ball can cross the goal line between the posts then yes it can happen but a goal would not be awarded so in that respect it can not happen.
If it goes out box, wind blows it back into goal and it goes directly into the goal, a corner is awarded.