DR UK
Well, IMHO, BA have operated different configuration 777-200's for ages.
Some have been 3-class (ie J/W/Y) and some 4-class (F/J/W/Y). The variant deployed has been a function primarily of the passenger mix on the route. Primarily leisure routes tend to have less demand for 'F' so have been 3-class. Primarily business, 4-class.
This aircraft has been changed from a 4-class to a 3-class configuration. Obviously removing 14'F' and 16'J' seats is going to release lots of space for additional 'W' and 'Y' seats, of which a percentage will be due to the 'densification' in 'Y', hence my comment about apples and pears.