The reason he's called a mysterious big shot is that this big shot with whom he was dealing was always shrouded in a layer of fog. Presumably due to some agreement, Commander Xie had not introduced him to War, and throughout the whole process, aside from exchanging greetings upon meeting, there was no additional communication.
War didn't pay much attention to this Lin Xiao— who cares who he is, as long as the goods are genuine.
Next, under the guidance of this mysterious big shot, he toured the tiny Crystal Wall Universe.