There is an information release for the area of the Gard that states road fatalities up by 69% since July, sad so many more had to die just to prove the 80kph was a farce!
Stats are never quite as simple as that.
I leave someone else to ponder and source the link.
It’s hard to say without a lot more data whether the increase is within expected variation and even if it is larger than one would expect it does not mean the 80kmph limit is the cause.
What is the experience in other parts of France?
Who knows but with good summer weather etc you would expect a reduction, after all that’s why it was done. 
I believe that was the justification, yes.
However, as Mat said statistics are never simple 
Reflecting on this… I note that local reports of each road death in my area … seem to highlight that the driver was either drunk or under the influence of drugs/stupifiants… more often than any other cause… 
The piece on the accident rate in the Gard mentions alcohol or other intoxicants as well as not wearing a seat belt and using mobile phones. They are saying “despite” the reduction to 80kmph though not “because of” the reduction in speed.
Quite so… around here, it does not seem to be the speed reduction that is the cause… 
Would they really say anything else? Can you imagine if they did? It does however show that despite the reduction it’s made what amount of difference? The UK and Germany two name but two countries with higher speed limits have less fatalities, all comes down to bad behaviour and bad driving, which French minister wants to be out of work really quickly by telling the truth, lousy driving! What next, 70kph?
It’s a newspaper so depends whether they want to dramatise and/or make political capital out of the change to the limit. I have no idea where they stand in the political spectrum or how rebellious “Midi Libre” is - possibly not very.
One commentator blamed bad driving - and I have to say that 15-20 years ago I did find the French driving to be pretty terrible - over aggressive, too close, too fast and a willingness to overtake in questionable circumstances. I vaguely recall a bit of a campaign on TV and a lot more police presence on the roads - perhaps those who have been in France for a while can tell me if this did actually happen or I am imagining it.
However I noticed that French drivers calmed down for a while, perhaps the effect has worn off?