It's very simple, the script interpreter starts with evaluating the output script being spent and when it is version 1 witness script it uses a different route for evaluation. That way it cutes the script in another method that checks the OP code to be in a certain range (including those disabled OP codes) and considers them OP_SUCCESS and simply returns true when they are in a Taproot script.
In a way it is bypassing the old evaluation where these disabled OP codes are rejected.