Here is the answer on the Polish instance directly from @ernest, kbin's creator. For reference, he was being accused of being a gun lover based on the name of the Polish instance "karab.in" and "magazines," as well as his Monty Python profile pic with a gun in it.

https://karab.in/m/fediverse/p/217281/The-reason-for-the-strange-naming-and-uncomfortable-images-on#post-comment-311421

Here are the relevant sections from Ernest on the origins of both kbin and magazine:

Hey, I'm the admin of kbin.social. The name "kbin" comes from the Linux "/sbin" directory - I've mentioned it multiple times before. The name of the Polish instance - karab.in - does indeed reference a rifle, but it's just a play on words, and it was actually chosen through a survey among other domains. It's simply easy to remember and sounds nice in Polish. There's no place for nazi bullshit on my instances.

On the other hand, the name "magazyn" refers to the virtual edition of a late 90s gaming newspaper :D

I found this

according to ernest it stems from /sbin. though one of the early instances was named karabin based on the karabine gun and thus shortened to kbin (or rather expanded from kbin).

(Ernest Wiśniewski is the creator of kbin)

probably a big bin for k's

I'd read somewhere that there's some sort of Linux programming reference in the name, but I don't know anything about Linux so I can't quite remember. Don't quote me on that, though