Actually, etaoin shrdlu is simply the order of the letters on the first two vertical rows on the left hand side of the linotype keyboard. [snip] So yes, it was a cipher - but for "I screwed up", not anything more sinister!

My point was that the reason for thie being in that position was that they tend to be (in that order) the commonest letters in the English language. This knowledge (of letter frequency) is invaluable when attempting to decipher letter-substitution methods of coding...