Hugo, this one has really got me thinking, but after studying the "behind you" picture you posted and reading about your recent Beddgelert walk I think it could be in the Cwm Bychan area as I think the picture shows the view down the Aberglaslyn valley towards the coast, with the lower slopes of Moel Hebog off to the right, and also the existence of wild rhodedendron in the area.
I walked the route many years ago, from Beddgelert North to Llyn Dinas and turned right uphill to walk back over to Cwm Bychan and down past the old pylons to return through the tunnels on the the WHR track (before it was relaid!) back past Gelert's grave to Beddgelert but I don't recall passing the bench so I could also be completely wrong!