I have read the transcript of this "Incident".
The controllers were aware from quite early on that the aircraft was taking off on the taxiway. They were following procedure (Amazing that they have a procedure that covers this!!) by not alerting the crew once take-off roll was comenced.
I totally agree with this. If there would have been one thing worse than taking off on the taxi-way, it would have been doing a high-speed Rejected Take-Off on it!!