The previous time he laid this trap on the Boar King, there were a few reasons for success. First was because Inala was equipped with a lot of knowledge about the Boar King, especially his character.
As the endgame villain of Sumatra Chronicles, there were a lot of details about the Boar King in it. Second, the Boar King wasn't in a state of battle. Hence, he wasn't using any detection means to perceive his surroundings.
Moreover, he had the arrogance as a Mystic Grade Pranic Beast. Even an Empyrean Tusk's full-powered attack wasn't capable of killing him. Therefore, he did not need to exercise vigilance. Thanks to it, Inala's trap worked.
But the case with the Millinger was different. The Millinger had been battling for more than two months already. So, all its senses were honed to the extreme and were sharp. As a result, its reaction time was instantaneous.