My best guess is that it would have been a chartered special. Normandy has just been granted a special status that will allow it to directly control the SNCF's services on five of its major lines, so perhaps this is a wishful-thinking TGV test run?
Unfortunately, Normandy actually only has 1 journey per direction a day run as a TGV and this is currently between Le Havre and Marseille. Indeed as abovementioned, this train is very well loaded during Norman school holidays but out of this, I have always found it particularly quiet and not particularly useful, apart from on Sundays when it is often the first train out of Le Havre. It is painfully slow, particularly along the shared RER section and it is generally no quicker, if you time it well, than a Le Havre-Paris (non-stop from Rouen), line 14 métro and a TGV which is first stop Lyon.
Having said this all, there still seems to be big political support in the region for faster Intercités trains with less stops, particularly on the Paris-Rouen-Le Havre and the Paris-Caen-Cherbourg lines, despite the SNCF saying they would be withdrawing trains from these lines due to lack of patronage at off-peak times.