Really not sure what happened there - did the strength indicator that shows your and opponent strength go overwhelmingly to his side? But I don`t see how that could have happened if you were doing so well... We will investigate - might have been some very rare bug issue, as we didn`t get any more reports of this issue yet.
And hey - at least you, and everyone else reading this know that you won. And even if you got defeat by mistake - it should have still awarded you some crowns, and u get to loot all the corpses on the map... hope this makes it a bit better. But yeah we`ll investigate.