The monk was weakened severely by the false monoshiro's illusion, but what did him in were the larger, savage species of queerrat. That clan was much larger and more human like in shape. The more spectacular attack he made, the more he obscured their outlines, making them look even more human-shaped.

He did himself in.

One might argue that Squealer's infiltrator sub-variant would cause the same effect, but they got close enough that it was pretty obvious from their ugly mugs that they weren't human.