I have seen this, have been taking a break until beta 4, (Other stuff needed exploring) essentially sometimes big creatures, or even wildland bosses decides to rampage through your lands and kill your people (or the ai's lands and kill the AI people).
I think its working as intended, although I can wonder how good it is for the game.
No need to say sorry though, but thanks! 
Sincerely
~ Kongdej
