Thanks! These are great points. I applied the correction you noted about the signs and changed the wording about the direction of evidence. I agree that the clarification about the 3 dB rule is useful; linked to your comment.
Edit: The 10 was also missing a sign. It should be −10 + 60 − 37. I also flipped the 1:20 to 20:1 posterior odds that the orcs did it.
Thanks, your confusion pointed out a critical typo. Indeed the relatively large number of walls broken should make it more likely that the orcs were the culprits. The 1:20 should have been 20:1 (going from −10 dB to +13 dB).