It is true. Read the reports. Why ADIRU 1 put out spurious signals is irrelevant: the system didn't isolate it and the pilots could not control the aeroplane... twice.
It's false. I went back and read the reports to refresh my memory. I don't know where you get the idea the the design of the ADIRU was supposed to isolate the spurious signals, but that's wrong too.
As for whether the ADIRU was a dud the 2nd Interm report clearly states it was not.
As outlined in the first Interim Factual Report, the ADIRU (serial number 4167) and an exemplar unit were subjected to a range of tests and examinations, and no faults were found that provided any information relevant to furthering the understanding of the accident.
http://www.atsb.gov.au/media/1363394...8070_ifr_2.pdf