As much as I would like August to be Bae I think that those promotional photos combined with the promo for the next episode contradict this theory. From the photos we can see that Bae saw the dagger and actually held it. In the promo August was looking at the picture of the dagger probably so that it would be easier for him to find it.
If he was Bae, he wouldn’t need the picture. Bae knew what the dagger looked like. Only a person who hadn’t seen the dagger before would need the picture to recognise it.