I never aim to dilute ship targets. Either out-rush it, trash your targets yourself and make money through actions or dilute his ship engine. You went for the third option in your game.
And I think that it's really the witch that won you the game. Silver+steward was definitely the right opening. You could have possibly opened with silver/embargo, because you saw him open with pirate ship, and embargoing the ship would have seriously diluted his engine while also helping with getting an early witch. That being said, steward is the overall better card.
Also, I don't think that game log tells you much about pirate ship.
The only improvement point I could propose in terms of ship management is that you would probably have preferred to have a second steward, in case he hits one of your gold. The likelyhood is very small, so actually getting 8$ with actions is not that important. But you don't want to get stuck with 5$ the turn after he hits your gold: you want to be able to buy a gold and return to provincing asap. Not to mention steward is just a plainly awesome card anyway. Did you have an empty turn to buy an extra gold or steward for security?