It is possible we are using the jargon in a different way. Technically, my printer was called a “kit”, but it required very little actual assembly, just bolting the main structural parts together. I also assembled a large format Creality which was called a “kit” as well, but again just required bolting together the big pieces. When I think of a “kit”, I am thinking of something that requires a little more than just bolting together structural parts.
The Prusa kit is a kit in every sense of the word.
Here are the assembly instructions: https://help.prusa3d.com/category/original-prusa-i3-mk3-kit-assembly_336
I had no experience with 3d printers but it only took roughly one day to put together.
The instructions were easy to follow and the machine takes care of a lot of the calibration stuff itself.