Isn't that a very simple substitution cipher (any clear text letter is substituted by two letters of cipher text, with a fixed one-to-one correspondence)?
And aren't they all amenable to very simple cryptanalysis, at least if the encrypted text is long enough, by counting how often certain letters appear, and then trying to plug in reasonable guesses?
"The model used “TRUPPENVERSCHIEBUNG” as the encryption word, as described on pgs. 214-215 of J. Rives Childs's “The History and Principles of German Military Ciphers, 1914–1918”"
Even if it isn't a simple substitution cipher as you said, all the model did was try a decryption key that had already been found and was publicly accessible. This is basically a nothingburger.
https://en.wikipedia.org/wiki/Substitution_cipher