[zerocrates]

You don't need to necessarily be looking for pilot error to want the recording. Maybe it picked up the sound of the plug separating and that could be useful. Maybe it records an alarm, a call from the cabin, whatever. Maybe the way they work the checklist for decompression reveals some problem that should lead to a change in the checklist. Maybe it corroborates or disagrees with the FDR.

Of course I think it's most likely that it wouldn't be that relevant in this particular case.