A sentence in the article is intriguing : it says both the captain , who was taxying ,and the supernumerary crew on the jumpset COULD not see the stopbars . Using "could" instead of "did" would indicate that either they physically from their seats could not see them perhaps because of the turns they were performing , or that they were not on.
But that could be just a journalist interpretation , who also apparently was wrong when he says that the crew did not know they were involved an incident until they reached London. , the ATC audio clearly shows otherwise. That they did not realise the seriousness of it, that I can believe, but they were informed they did not follow the taxi instructions.