Mai Fei didn't show up himself and let Nian Jincheng come, not because he wanted Su Liang to believe that everything was Nian Jincheng's idea.
The decision maker is surely Mai Fei. No matter who passed the plan on to Su Liang, this is clear, and Mai Fei himself knows it.
Nian Jincheng, referring to Mai Fei's plan as "our plan", doesn't change anything about the matter itself. However, Mai Fei cares about Nian Jincheng's attitude.
What Mai Fei really wants Nian Jincheng to do, by commanding him to come forward, is not to inform Su Liang, but to convince her to act.
Anyone could deliver the former information.
The latter, which is the key, can offend people and has a very high possibility of failure.
If the action fails, Nian Jincheng will bear the consequences.
After Nian Jincheng met Su Liang, following Mai Fei's instructions, he completed the first step of informing her.
