I lost, thanks for the win

Went back an a saved game the other day and decided to play through and conquer everyone.  As I neared my goal I realized that the last enemy was going to finish casting the Spell of Making before I could take him out.  I let the game finish and took my loss, but instead of getting the message that I lost, I got an achievement Leader of Men for defeating all my opponents.  I never got a message saying the last opponent was giving up (why would he after all).

If I was an achievement whore I'd love this little glitch, but it does seem a little on the cheap side to lose and get the achievement anyway.