Xiao Nan was very smart, otherwise, he wouldn't have taken down Demon Baal after accidentally joining[Solomon Plot].
Without preparation or support, he successfully passed the test of the demon god with his intelligence alone.
Even while enduring the pain of his body exploding into bloody lumps, he could still remember the entire chess game. This kind of calculation and analytical ability was not something that average people could do.
If it were Li Changhe, he probably wouldn't have a solution other than cursing. He doesn't know anything about western chess...though he could probably try his hand at Go, but only after taking back a few moves.
When it came to the efficient flow of thoughts and combat, Li Changhe didn't hesitate and could even make some eye-catching moves. When dealing with the rat-man lord, he could coordinate with Moon God and Mo Mang to perform a perfect ambush and cover.