Whether it is a beast or a human, one would always fear the unknown and wouldn't foolishly tackle it.
There's a reason why Mark arrogantly attacks the opponents that offend him. Why? It is because he knew that he would win for sure.
And at the same time, since he couldn't inspect the details of his biological mother, he proceeded cautiously with a different approach even after capturing a beast king of the eight-circle realm. Of course, that can be changed once he captures this demigod realm beast but the possibility appeared to be a little bleak, at the moment.
Similarly, Lan Ju could neither sense the strength of the visitors nor could he recognize the exact nature of the Protos energy present in the daggers held by Alina. Hence, it shouldn't be a surprise if he turned a bit wary of them.
