I can understand, if its a parallel runway, but parallel taxiway its a serious breach, especially, the blue taxi way edge lights if its a night time
I think we all have exactly the same thoughts. However the very fact that they were taxying along blue and green lights for a long time already might worsen the situation, as a colleague of mine recently argued. If all you see when taxying out is green and blue taxiwaylights, and for some reason you are so distracted that you think you are on a runway, then there is no give away: your mind will be accustomed to the green and blue, the lights continue to be green and blue, all seems nice and peaceful. Sounds a bit fuzzy, but human psychology is fuzzy. This mistake for instance, would have less a chance of happening if just for the sake of argument, taxiway B had purple lights.
Then there would be a change in stead of a continuation of the same, triggering the mind to be more alert. Of course, we are talking about a situation where a lot has gone wrong already.
Consider also that it was not quite dark yet (as I understand/speculate it at least). So it would not be absolutely necessary to expect a full row of white runway lights. Keep that in mind! So, you don't necessarily expect full rwy lights, there is no sudden change in lighting...crew severely distracted maybe...
Again, very fuzzy, but the answer to a mistake like this will be fuzzy anyway.