The answer gives no evidence that the "x" is truly arbitrary and I am not inclined to believe it. "x" is one of the letters of "hexadecimal" and the letter-name

The answer gives no evidence that the "x" is truly arbitrary and I am not inclined to believe it. "x" is one of the letters of "hexadecimal" and the letter-name sounds very much like "hex". Are we supposed to believe that Thompson or Kernighan or whoever it was picked a random letter of the alphabet and it just happened to be one of the two letters ("h" would be the other) with an obvious mnemonic connection to "hex"/"hexadecimal"?