If they got into a degraded flight control law (eg something similar to A320 direct law) and were in IMC they could well end up in a pickle like that, all the more so if instrumentation was degraded too as might happen with a big electrical failure, only regaining control when in better visual conditions. Their situational awareness was so poor loss of instrumentation to a significant degree must be a strong contender. If they were in degraded f/c law on standby instruments - that's a tuly nasty place to be in an Airbus, and I imagine in any other type too.
No doubt we'll soon know.