It's a promotional outfit. The pose is the same as Miqo'te whom the outfit is taken from. This really isn't any different to the Cloud outfit they're giving for pre-ordering. Heck Yuna isn't really even in line with Lightning's personality but people don't seem to be kicking up as much of a fuss over that promotional outfit.

I think people are reading way too much into this. It's not like it's being added as a canonical element of lore or a development of Lightning's personality - it's a promotional outfit. Nothing more. Nothing less.