Round table

"if he used battle magic or any other magic that, in one way or another, inflicted any damage to the opponent"

Following the spirit and purpose of this rule, retreating should not be allowed; I agree with AlexR. You USED battle magic; resistance is an opponent's feature – why should you be penalized for that? For the future, a clearer and more unambiguous formulation would be: "
"...if he used magic (battle magic or any other), which can inflict any damage to the opponent" – and it would be even better to specifically list the exceptions in the explanations – the magic that, when used, allows retreating... IMHO.