He ends up unknowingly actually properly setting himself up for the full harem of the sequel's heroines. And the MC of the first game is another guy who was reincarnated. But that guy never really played the game. So the MC ends up having a double harem, saving not just the girls in the sequel, but the girls in the game. Yes, he behaves in your typical I'm just going to be the mob and let the hero have his harem. And even after finding out that the Hero is another reincarnated guy, tries to push him to complete the route of some of the girls because he doesn't want to see them have their bad endings, despite the fact that the reincarnated Hero is a one girl guy.
At least from what I remember. You can read the novel yourself here
https://storyseedling.com/series/92962/