Nether Flame gave the exact same reply in the same tone and with the same nonchalant attitude. This made Loki confirm his suspicions about what was going on.
Nether Flame was a rank 7 cultivator and an old one at that, so he should know how much he pays for life-leech and what the limit of the size of Cave Heaven for rank 7 cultivators can be. Yet, he is lying with a straight face to Loki that he doesn't know.
Since it was obvious that he was lying, Loki was able to glean the underlying information from that sentence. Without being stated explicitly, he was able to ascertain that Nether Flame didn't want to tell him the answer for unknown reasons.
In fact, the most likely reason for withholding information was that Nether Flame didn't like him and didn't have an obligation to answer his questions.
If it were another fresh divine being, they would take the hint and give up at this point. But Loki still wasn't willing to let things go.
