for the discord, maybe he just want to control the population who's going to be there; also less people means less moderation work.
Its probably a double edged sword; this way he only gets people who are really invested in the game and likely have the same vision, which cuts down on the noise. However, there is then the risk of a lack of diversity leading to a niche outcome with potentially serious lapses in some aspects. May not be fatal if your niche is still enough of a market to be economically successful. However, it can still lead to a lot of noise in reviews by people who don't fit the demographic and bought it anyway, which eventually may turn off even your target audience once it gets bad enough. e.g. About the time you hit "mixed" on Steam.
Man, I am glad I am not an indie game developer; its a fucking thin tightrope to have to walk.