Brand image would definitely be important, but not for the Chinese market there. I doubt that many people in China know who Hugo is. I even know quite a few people who don't know what Google is. If I have to guess, it's for building infrastructure (connections) of Xiaomi breaking into the North American market. Xiaomi's CEO is extremely ambitious and there is no way he'd sit out of THE most profitable mobile market in the world. So he starts by making a high profile hiring first, good PR move and a practical move.