The most that the ATSB was able to determine was that the data corruption was basically akin to a C++ reinterpret_cast of "altitude" as "angle of attack", causing the 37,000ft or so altitude to sporadically be read as a 50 degree AoA.
The issue was not definitively traced to cosmic rays or another root cause.
Once Airbus knew what the problem was, they were able to detect and mitigate it with a software update. They didn’t fix the hardware.