The captain of a Qantas flight that suffered two computer-generated pitch down events, injuring more than 100 passengers in 2008, has questioned Airbus’s explanation for a similar incident on an A320 that led to the grounding of 6000 aircraft for a software fix. ...... Kevin Sullivan who captained flight QF72 on an A330 in October 2008, said there were many questions to be answered with respect to the A320 issue. ... ..... He said the uncommanded drop in altitude he experienced on flight QF72 was never fully explained with the Australian Transport Safety Bureau ruling out solar radiation after exhaustive tests. Paywalled article

So EXACTLY how was it determined that recent A320 event was caused by cosmic rays. I seems tha tit is not possible to make such a absolute determination.

It is possible to say however , that cosmic rays could cause such an event.

But how is it known that cosmic rays caused the recent A320 event and not some other error hidden in the software.???