The disguisers in the Underground City have contacted Sidney.
Therefore, Sidney should already know that Marcus has been to the Underground City.
However, he also knew that the Underground City could shield all electronic devices, so even if Marcus knew the secret of the Underground City, he wouldn't bring any evidence with him.
As an orc, his words wouldn't be believed by the Plant-Man.
But Sidney would never know that Marcus not only discovered the secret of the Underground City but also recorded everything.
Auspicious and Lucky were not ordinary artificial intelligence.
With the addition of Cheney's designs from his hometown, Auspicious and Lucky could still function under extremely restrictive electronic conditions.
Moreover, they could even communicate with each other under extreme circumstances.
Of course, even though Auspicious has been found, Sidney was still not at ease.