"It looked like they were fleeing the scene when they were ENGAGED"
Does not agree with:
"I did not see anything that indicated they [Blackwater guards] were fired upon."
Now, either some type or form of combatant or group of combatants engaged them or not. If you are in a combat situation, or an armed confrontation, or some sort of danger zone, "engaged" means "under some form of attack".
So, which was it?