I never used such a formation (not even something close to that) to play against a 3-4-3. What orders did you use?
Possible explanations for why he lost by such a large margin are more likely to be combination of those: wrong orders, inferior quality, players placed out of position and bad 'roll of the dice'. Your formation may also have countered his formation; I did a quick analysis of the formation to see how appropriate it might be for use against 3-4-3, and the result is decent.