Duo top is beaten by the top laner playing safe and scaling.
Why is a jungler even in the dang meta if duo top is so strong?
Interestingly, 2top 1mid 2bot was a standard all those years ago very early on in League's history (Riot themselves even resisted jungling as a role). Things changed and Riot gave in eventually because Jungling is the stronger strategy.
That guy in your game had it wrong, it's not that "you get more cs", it's that they don't. The thing about gold is that it is stronger together than split up; A Champion with an Infinity Edge and a partner is much stronger than two players who only have two incomplete weapons on each.
Duo Top gets less gold and experience per player while the team with a jungler gets to take advantage of a greater amount of the limited resources on the map. Against a duo top, the team has an even greater advantage; a jungler is not only able to capitalize on the jungle resource, they can take the enemy team's resources, gains map control, take advantage of enemy positioning, gank unexpectedly, and take an enormous amount of objective control. They can force the top laner away from CS but they lose the ability to contest objectives.
What the top laner does in this situation is play safe, take what farm they can, not die, and protect the tower as long as they can. Duo top will rely on using their early advantage in one lane to snowball. Your objective is to deny that; to make them waste resources and man-power on trying to take you down but you preventing them from getting advantages from that. You can allow your team to scale harder because disadvantaging you at top costs them disadvantaging their other lanes and the other four members of yours gaining one.
