We are shown Mr Lang as someone who is so ravaged by shell shock that's his hands shake so much he cannot replace the screw-on lid of a brass polish can. Yet the next time we see him, he's sewing by hand such an intricate stitch that those around him are amazed at his fine honed skill. If he was unable to screw on the lid of a can, how could he possibly manage to hand sew like a professional tailor.
Although it is coined in Shakespeare's "The Tempest" Act V Scene I, the expression "Brave New World", as used by Lord Crawley in the last scene with that meaning comes from Aldous Huxley's famous book, "Brave New World", which was yet to be published on that date. The book has been published in 1932, although the date mentioned in the episode is April 1917.