For two men living on exact opposite sides of the world, though yes one would be awake while the other one is asleep, the question of who is the dream and who is the dreamer would not arise - since for a third of each day, BOTH would be awake.
At around the 9th, 25th and 51st minute marks of the film respectively, while Khai was supposedly on the Shanghai metro, one could clearly overheard the station broadcasts were in Cantonese and not Putonghua. As a matter of fact, those station broadcasts were Hong Kong MTR station broadcasts.