I think it's a good idea to have an out of game conversation about it to clarify what the expectations for the spell and possible enemy behavior, and the social contract of PC death.
Like others I don't see anything in the spell that would prohibit it, and smart enemies should use smart tactics, though I'm not sure if these were smart tactics. It sounds like the bad guys split the party just so they could give a beat down on one enemy who was running away. Why wouldn't they focus on the enemies who are still putting up a fight and threatening to kill their allies?
It's possible that your player's perception that you "cheated" is not that you broke the rules of the spell, but that he felt like you were picking on him for meta-game reasons.
Like others I don't see anything in the spell that would prohibit it, and smart enemies should use smart tactics, though I'm not sure if these were smart tactics. It sounds like the bad guys split the party just so they could give a beat down on one enemy who was running away. Why wouldn't they focus on the enemies who are still putting up a fight and threatening to kill their allies?
It's possible that your player's perception that you "cheated" is not that you broke the rules of the spell, but that he felt like you were picking on him for meta-game reasons.