Both that it's stupid and doesn't seem to make any sense. And that he's so detached while he's doing it-- he's not angry, not defending anyone. It's so wastefully brutal a way to shut the creature up. Is there any reason for him to kill it? The only thing I can come up with is, if the hive mind of the Bringers constitutes something he sees as a threat.

Yeah, that might be an explanation.