Didn't see it myself, obviously - bit far from Dartmoor for that one - but I've been doing paranormal photography for going on 40 years now and triangular craft sightings over large bodies of water do seem to cluster in ways that are hard to dismiss. Lake Michigan has a decent history with this sort of thing.
What I'm curious about is whether anyone managed to get photographs or video. And if so, what time exactly? The reason I ask is that lighting conditions and the angle of whatever light source is present can completely change how a craft's shape reads on camera. I've had shots on the moor that looked like one thing entirely and turned out to be something far more ambiguous once I started looking at the metadata and exposure details.
Were there any other witnesses nearby who could corroborate the shape? Triangular is quite specific and I'd want to rule out the usual candidates before getting excited about it.