There's a change in picking images/videos now. It uses WP8.1 picker and also allows u to pick from OneDrive or some other Location. Neat and Snappy.
http://imgur.com/a/SU3Yw
I guess this is a drastic change as earlier they had to keep log of all images which would mean they were indexing everything at app level I guess. So this might have affected overall performance of FB app , and if they were indexing those in background then all that means it would take lesser footprint when in background => overall performance.
Or maybe it's just a placebo for you
I guess now WhatsApp can also use the same approach and give a good win here (finally we can pick OneDrive pics or even pics in other folders). WP8.1 actually changes a lot of things and now we just need better phones and Apps made