Is it possible in regular Heroes III to sort captured castles by type?
No.
And how did the enemy hero move without an army? I couldn't believe my eyes when I attacked him (and immediately won, of course).
Here is how This is a bug in the game. But everything might be much simpler. The AI gave a creature to the Seer and exchanged it, leaving itself without an army.
За то что нейтралы не бегают за единичкой, для меня это уже стоит того