Transformer solves a Seq2Seq problem just like RNNs. All Seq2Seq problems need not involve a language. In this case teaching on ARC puzzles doesn't mean what he trained is now trained on a language which will be English(or any other language) in this case. So, does his training successfully models "English as a language" -> No. This implies it is not "Large" and has not modeled any "language".