Ji Ning's heartworld projection covered the entire Sacred City, and so his voice naturally echoed throughout every part of it.
In truth, Silksnow Fiend Palace wanted to contain and minimize this disturbance as much as possible. Just the very fact that Daolord Darknorth dared to so flagrantly attack them was already a loss of face, even though they would kill him in the end. They naturally wanted fewer people to know about this matter! Alas, as soon as Ning's heartworld projection descended they knew that there was no way to keep this secret.
Ning, however, wanted to 'kill a chicken to scare the monkeys' in a display of force. He wanted to let everyone know just how powerful he had become. Naturally, there was no need to keep anything secret.
"Absolutely dominating."