Okay, let me ask you a simple question:
What would it have cost you to wait 3-4 ticks for their armies to return, if it was over? Because all you've said is that the conflict was done and a cf was offered. That doesn't change that they were hostile with an in range kd.
Nothing? That's why you wait and be respectful of hostile. The only reason to not wait is to exploit those provinces with troops out / the inability to retal immediately.
The fact that troops were home soon makes what you did more ridiculous, it doesn't justify it.