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.