The tanker had the right to be there: she had just left the loading berth and aiming to sail diagonally to the correct side of the fjord. I imagine that she would have not moved off the berth when she did had she known the frigate was coming down the fjord towards her at 17 knots, but the lack of AIS on the frigate meant she had no way of knowing in time.
The navigators on the frigate bridge had obviously lost situational awareness. It is easy, when in training mode, to get in to a 'bubble', and concentrate on completing the set task, while forgetting about the real world outside. Even a last minute 5 deg alteration to starboard would have saved her, had the navigating officer listened to the tanker, but switching on the AIS and / or slowing down earlier would have been even more helpful.
2 large 'sheerleg' lifting vessels are now en-route to lift the frigate off the sea-bed (from 20 m down) and onto a semi-submersible vessel. However, there is worry that the frigate is unstable, and may slip into deeper water before they can get her lifted. Apparently she has almost 500 tons of fuel on board.