What a surprise move. This is definitely something what I miss in my MP battles. I roughly know the terrain, enemy brigades and their initial placement, timing of the reserves, their entry points and most successful enemy strategies for all MP scenarios. No surprise at all, no reality.
This was unexpected like the real life. I suppose that both of you will remember this game long after many another MP battles.
In spite of this I voted for cheating but only because the one of you was unaware that something like this is even possible to do.
The same question is if it is fair to protect the flanks by the edges of the map.