I agree that the pedal design, human error and floor mat problems are much more likely causes. I don't claim it was a software error for sure. My understanding is that indeed no specific software error was identified, but it also was never ruled out for sure. Neither of the two links seem to contain anything to that effect either.
To my memory, the podcast lays out a fairly comprehensive argument that it was just human error in the case of mechanical problems (as we'll as noting the car computers in all the cases show the brake wasn't pushed), and back it up with decades of research showing that this is a common problem, so that's about as close to definitive as you can get in this situation IMHO.
