[snarkconjecture]

No, it's ^J because `J` is 0x4A in ASCII and `\n` is 0x0A, just as `I` is 0x49 and `\t` (tab, ^I) is 0x09.

In the stone age, pressing CTRL flipped that bit, so ^J is literally "ctrl-J".

[kps]

You're saying the same thing. vi uses ‘j’ because the ADM-3A printed ‘­­↓’ on the ‘­J’ key because Control-J is newline because the code is J with a bit flipped because bit-flipping was practical on an electromechanical teletype.