I think this is a common thing to happen to less experienced AI commanders.

I've fought lots of AI commanders that wait and lead their troops.
I've fought many who withdrew all their forces just by seeing that my force was more powerful although not in troopsize and so on.

I play julii campaign and usually when i fight enemy AI it's just some captain or lowlevel family member. But the times ive met 5 star and more they have often been really good.