This was something I’ve noticed in my time playing Pokemon Go. As with most people, you assign your buddy for something that you struggle to get candies for (my current buddy is Lileep). I caught one Lileep just when it was released, and have never seen another one in the wild. About a week after I set it as my buddy, I hatched one from an egg and it boosted the candies by 15.
I feel like I’ve noticed this trend before, that you’re more likely to hatch a Pokemon that is set as your buddy. I assume there isn’t actually a correlation between the two, but I’d be interested to see if anyone else has noticed this in their time playing Pokemon Go.