Do gnomes kill other gnomes? If so, how?

I ran across a strange situation. I was looking at a gnome who had not been very helpful in a recent combat, and realized that there was a Kill entry for a gnome in his list. How did my one gnome kill my other gnome?

Maybe I need to create a focus group to train these fighters that there is good touch and bad touch, and killing your buddy is very bad touch!! :P

But really, I can't figure out how this happened given these two screens:

First, I saw that in the history, he had bled to death. Not a very unique situation for the difficulty I am playing at.

But then in my Current Nurse's Kill list...

At least he was notable?!? I did not know this was possible. How do I prevent this?