Runways are my business, as those of you that visit 'Tech Log' will know. I'm not a commercial or ATPL pilot, nor am I a human factors specialist or air safety investigator.
But as I look at it, he landed on a runway. It may be convenient to call it a taxiway or more likely it is called that as some weak military subterfuge, but that thing is a runway.
I went to the proper Google Earth and measured it as 45m wide, which is the civil requirement for that aircraft. The ends have been beefed up in concrete (which is good runway engineering for that application), and the western end has a proper runway turning node.
I'll leave the discussions about training, markings, local airport experience, and kinked instrument approaches to those better qualified then me. The comments about marking the two runways there as "L" and "R" make sense to me in a normal civil sense. The juxtaposition of the 'declared' runway and taxiway relative to the terminal is indeed there. However I find that I understand the Greek engineering better from the perspective that they are clever and subtle engineers.
The length here (of the taxiwayrunway) is 3075m. This is not just a runway that they landed on, but a very serious runway that they landed on. And given its location, of serious intent. And of serious strength as can be seen from techniques which I will not discuss.
I don't think my point can materially help the Thomson pilots. I have learned something of Greek airports, both civil and military, and a little of their design and documentation approach. I would not expect anything to emerge on paper which confirms my assertion. But if it is some small comfort to the pilots, they landed on a runway.