Se Lang initially felt bad vibes coming from the castle. Even before he entered it, especially after he saw how ugly it looked from outside the castle gates when Pyro Jack was talking.
But that sneaky Jack O Lantern lied.
The moment all three entered the castle courtyard, the gates behind them closed shut fast as if it closed its mouth to keep its prey inside and never allow them to resurface again. Se Lang noticed the door closing after taking a few steps inside but he was unable to react in time because of the Gingerbread Knights that blocked the gateway.
When the gate closed, the dull interior design of the courtyard turned into something desolate and broken. It was an illusion that Pyro Jack was barely maintaining till now when the cultivators stepped into the 'castle' courtyard.