They are in China right now, and the finals are in China, I`m assuming they will just stay in China instead of going back to Serbia and coming back again. The final starts only on August 2, they will get 10 days off, I`m assuming that`s why they will play this friendly game.
Just to refresh, the Finals Round in Nanjing, the capital city of Jiangsu Province, kicks off on Wednesday, 02 August 2017... so it's wise for the far away team like SRB (practically all would-be contestants) to spend around one week or so in Jiangsu. Moreover the players may be relaxing and taking rest instead of wasting time to trouble flying to and fro..,. and there are many cool places for sightseeing around there such as the West Lake, the ancient town Wuzhen, and so on...
Or simply pick from this list: https://www.travelchinaguide.com/cityguides/nanjing.htm
basically just countless ways to fill up the extra week worthily