The photograph provided in the first post is very confusing, and it made it difficult to understand the whole scenario. I checked the airports charts and this confirmed the confusion. In the photograph the only strips marked as runways are 16L & 16C. Taxiway T 7 RW16R are both bare of conspicuous markings. How old is this photo? I can't believe RW16R could have been in use when that photo was taken.
However, what it does show is the significant difference & contrast between the markings of taxi T & RW16C. . What I remember, when this happened at LGW, is that the taxiway was sometimes used as an 'emergency runway' and had some runway markings on it. It was NOTAM'd as in use as taxi or runway. But, on the day, Murphy was awake.
In this case I also see that sunrise is at 07.56 and the landing was 08.33. Variation is 16 degrees. Would that have caused any sun effect?
I suspect the only people who can answer the curious are the pilots. What always surprises us all in these type of "why did they do that" discussions is that 2 people made an error. This was not a high pressure/stress moment where a cockpit gradient could have been in play. I assume this change was actioned with time to spare in good visibility. Hm????? What was the crew's roster before this landing?