With development of the Comac C919 lagging behind, this order will fill the gap until their own aircraft reaches the standard of a realistic alternative to western products. Airbus will undoubtedly need to source and produce components in China which will give a lift to their aerospace industry and help it gear up for domestic production.
The C919 is still years away from being a serious competitor on the international market but with the massive growth in domestic aviation it could be a realistic proposition for Chinese airlines, especially if the government "suggests" that they buy it. A version without western equipment could be offered to countries such as Iran which are under sanctions.