Your friend doesn't know chess very well. Or is a super-grandmaster.
That's right. Memorizing openings in chess will no get you very far at all. They only become helpful in chess once you are already very good at it. When learning chess the best way to get better is to study tactics. If you play a chess opening perfectly and your opponent doesn't, all you will have gained is a slight positional advantage. This won't help you at all if you miss a tactic and are suddenly down a piece.
I think you actually can compare dominion to chess in a way though. While each dominion game has a different kingdom, each game of chess will usually reach a unique position. Analyzing a chess position is as important as analyzing the kingdom. In some sense memorizing the various engines and BM strategies in dominion does help you. However, experience seems to me the only way to get a good sense of how many of what cards you need in your strategy.
Another analogy: In the endgame of a game of dominion you sometimes have to calculate quite a bit to decide whether to buy that penultimate province, or if it's worth buying that duchy right now. this is especially true IRL without point counters. In the endgame in chess it is often worth it to spend quite a bit of time calculating it out, often as long as 15 minutes. This is from 8+ years and hundreds of tournament games of chess experience.
