As far as i know nothing in TF 1 is KSable. and i've had this happen about... 6 times now... unfortunately i couldnt get any on SS :/
Edit: re-checked the rules:
◦A monster "belongs" to another player if it is attacking, being attacked by, trapped by, or following that player.
◦Monsters that give the MVP sign when killed are exempt from this rule.
nothing in TF 1 is an MVP so... ya no its not KSable...