genuine question, NOT criticism of the pilot...
Unless there was a considerable time saving (e.g. POM from the south) why would an operator or pilot prefer a DME arrival over a RNP Runway approach?
Lack of approved equipment? Pilot not approved? Company 'culture'?
The DME arrival allows you to dive down to 1700' at 15DME, so you'll get to 1700' at about 9 miles from the threshold. If you can find a gap, with the cloud reported broken at 1100', overcast 1900' then you can call yourself visual and proceed VFR. That means you can descend visually to 500' AGL - if you have the VFR minima of 5km visability and remain clear of cloud.
If you fly the RNP approach as a straight in, then you fly the constant 3º slope down to an 800' minima (at about 2.5 miles to the threshold), and once visual you only need 4.5 km vis on this approach. The DME is easier to fly (less lateral tracking) than the RNP (depending I suppose on how sophisticated your autopilot is).
Given the cloud, it looks like the pilot thought that option A would be the more assured way of getting visual ... the problem was that it very much looks like he didn't maintain VMC.
The pilot stated that visual contact with the runway was maintained throughout the final approach but, due to crosswind from the left and as the aircraft tracked into the lee of the mountain to the north of the runway, some realignment with the runway was necessary.
He decended to 400' AGL at 3.3 DME when a normal approach path would have him at about 1000' AGL. He was 125m right of centreline at 1.5 miles to go, increasing to 140m right of centreline at 400m to go, and talking about looking at islands for height and tracking information - that's not someone visual with a runway (and if he's not visual with the runway then he doesn't have the required 5km for a visual, not even the 4.5km if he had conducted the instrument approach) and he should have climbed to join the missed approach procedure once he lost VMC.
Regardless, he pushed on with the (now illegal) approach and once he finally saw the runway just 400m away slammed in a left/right turn combination that had him overshoot and land on the grass - then said that he began a go-around, but cancelled that when he felt the touch-down (also a bad decision - once you begin a go around, you commit to it.).