Upon deciphering a part of the given C1, you could see there's tool 4, prope 10 (for property), semin 3 (for seminar), and that would be enough for you to make out the rest of your 12 word seed phrase (given that you decipher the rest of the cipher blocks).
You only need the first 4 characters for each word. "prop", "tool", "semi". I think he has clarified this already.
I also doubt that the words are scrambled, like "property" -> "pr_o_p", "seminar" -> "se__mi". He's bragging about the puzzle's simplicity, and that's too complex.
If "property" -> "pr_o_p" and all words was scrambled like this before cipher it will be hard enough to use some "simple rule" to decipherd it back, cause you also need to remember in what row what exact symbols was fake or navigation symbols and what symbols was from seed. Or that "simple rule" isn't so "simple" and has several points in it, which are based on the author's imagination