Because wait() is defined in Object. And the compiler is smart enough to realise that any object that ends up implementing Floral (or any other interface) is still an Object, and so it will always be safe to call any methods that are defined in Object. Similarly, try toString(), equals() etc.
Actually the wait() method is in Object class. We can call Object class's methods in any class in java. That's why it is not giving any error or throwing any exception. We can call Object class's method on any object in java. So there is no problem in calling wait() method on interface's floral object.