Ryanair on grass in Poland - Taxi incident

[Checkboard]

A summary, then. The aircraft became bogged whilst taxiing off the runway. The pilot taxiing either:

1. Deliberately taxied off the hard surface. Almost impossible to believe.
   
2. Was distracted (along with the second pilot) to the extent that neither was looking out the window as they approached the end of the runway. Possible, but unlikely when you are appoaching a 180 degree turn.
   
3. Had an obscured view due to conditions of the time (e.g. glare) If the view approaching a 180 turn was that obscred, they should have stopped.
   
4. Knew their ICAO airport markings, and believed that they were taxiing towards a permanently displaced threshold, allowing them to cross the threshold and turn beyond it. As the runway is correctly marked, this error would be one of having such a strong mental model that the imagination "drew in" the missing lines. This is possible if, say, the runway they use most often is in this configuration and they were compacent (perhaps through fatigue.)
   
5. Didn't know their ICAO markings, and thus saw the correct picture out the window, but didn't understand that they were taxiing onto a suface not capable of supporting the aircraft. An error in professionalism? Perhaps better training? Perhaps better markings? Perhaps a change in the ICAO standard?

Given some of the responses in this thread about markings:

Looking at the video the aircraft was on the turning pad at the end of the runway.

but it also looks like a stopway...which of course you CAN taxi on.

When the portion of the runway is intended to be maintained as a stopway, chevron markings should be in place. This is also the same with EMAS. There should be yellow chevron.

I expect an area to be marked off if i can't taxi on it.

here was no indication that the area was not a "load bearing surface". Chevron markings, taxi side-stripes (yellow) or crosses should be used to make clear that this area is not part of the manoeuvre area.
A steady white line does not per definition mean that you can't cross it.

... I wouldn't be surprised if (4) was the most correct answer.