OK, I am now retired, but I have to say that my choice of rest, as Captain, was influenced by the forecast weather.
Not because I doubted my colleagues abilities, but because I didn't sleep well in the bunks at the best of times, and turbulence didn't help me sleep.
I accept that for some, sleep comes easy - turbulent or smooth, but not for me. So for some Captains, they would always choose last break, to be best rested for the landing, whereas I would choose the rest break that gave me the best chance of some shut eye.
With that in mind, if I had been Captain on that AF flight and had had the choice of break to take, I would not have chosen to have the break on that section of the flight.
I have to add that I know nothing of the AF SOP's and infer no criticism of the Captain. The company procedures for transfers to fleets should be robust enough to ensure that people occupying the seats in the cruise (and at other times) should be adequately trained and qualified.