Is that proven to be an actual thing, I've heard people say it's deliberately generated like that, but it's always seemed to lay more in the conspiracy theory area then the hard proof area.
I'll say from my own experience it's always seemed to be a toss up, sometimes my neighbors are friendly, sometimes not. I've not noticed a particular trend, so I'd assume it's random, but I've not paid enough attention to be sure.
In my last game (last game where I wasn't a no diplomacy civic at least.) I was slaving despots and had to my west three empires, 2 friendly religious nations and a not very friendly religious nation, to my south a not very friendly religious nation, to my east a warrior nation who could have swung either way friendly or not, but I put the work and bribes in to make them friendly. Similarly, the friendly religious nations could have allied up with the unfriendly religious nations, which would have made them unfriendly to me, but I made friends with them before they did, which made them unfriendly to the unfriendly religious nations.
Ultimately it was a very friendly galaxy for those willing to put in the effort to make friends, almost the whole galaxy (eventually the whole galaxy outside of places I owned) joined a religious themed federation, even I did for a time, but the pacifism of the group eventually caused me to break away from them and conquer the unaligned nations for slaves, that made them hate me for about 200 years, but eventually I made friends with them and rejoined the federation once I had killed the Crisis. So the game ended with everyone outside of two surviving AEs in a big friend group. If I was materialist I probably would have found the place a lot less friendly then I did though.