MythicMobs actually just checks whether that class exists.
They tried obfuscating it a bit (notice the single-letter difference between the two fields:
Code:
volatilityHandler
volatllityHandler
Mythicmobs actually checks for this class with a Class.forName call, which fires the static block in your screenshot; if that static code runs, then Mythicmobs has searched for the class and the crack works. If it never gets called, then the static code won't run, and the message won't get printed.
So if it gets printed, it works, as seen here.