The spell description states:
"Engaged units carry over any hits scored into the first round of combat and hits caused by the Volcanic Eruption count as having been struck in the combat itself."
Would that have had a bearing on how the end result of your combat would've been? As in, due to the fact that the hits are counted as having been struck in the combat phase, even though your troops didn't actually strike anyone, are you still in combat etc, when the spell effects actually happen??
Or am I reading too much into the last part of the spell description - should I just be thinking that the hits are carried over - as per normal - into the combat phase but as you killed the stand/s with a spell, there is nothing to carry over into the combat phase and therefore no combat has actually happened?