Earlier, when all the Core Disciples were giving half of their Night Demons to Felix, Ethan was the one to hand over the Night Demons from his team.
Ethan made it look like he was gifting the Night Demons to Felix, and thus, his Special Talent [Gift of Eternal Pursuit] was activated.
From that moment, Ethan could sense Felix's location, and while entering his abode, he was quietly keeping an eye on him.
That's when Ethan sensed Felix leaving the Sect, and he roughly guessed Felix—or to be exact, the Ancient Evil Spirit's—destination.
Since Ethan was waiting for an opportunity to deal with the Ancient Evil Spirit inside Felix, he felt the time had come much sooner than expected. Without wasting any time, he rushed out of the Greenfire Sect.
...
"What is the purpose of…?"
At the entrance, one of the guards wanted to know Ethan's reason for leaving the Sect; however, when Ethan showed his Core Disciple's Jade Badge, the guard swallowed his usual question and let him through.