This has been mentioned in the PR as well. He assures that he will fix the spec and implementation to reflect this. The previous version was using a hard-fork, and the normalized transaction ID is computed only considering the non-malleable parts of a transaction. In other words, signatures are stripped before computing the hash of the transaction. Tier Nolan via bitcoin-dev asks if the proposal is recursive, to which Christian explains that for non-coinbase transactions, sigScripts should be replaced with empty strings and txids in TxIns should be replaced with n-txid for parents. The second step is recursive starting from the coinbases. The rule is that txids are what they would have been if n-txids had been used right from the start.