"The core of Key is based on a ....."

So either it was called key, and Kei is a homophone, or visa versa, thus the mispelling or 2 translations from a different language, or they really like Kei cars ?

Or autocorrect interfered

It's one of the readings of the Japanese character 軽, which means light (as in not heavy). That would be my guess, but I can't say for certain.

The same kei (軽, lightweight) as kei-car, maybe: https://en.m.wikipedia.org/wiki/Kei_car

Its Dutch it means 'stone' or 'rock'. Its often used as 'kei-goed' meaning very, very good. So in Dutch its actually great language name!

It's Kei (romaji) meaning light. I don't remember where I get that name, but I think I was listening to some random music.