It was not really an ATC strike but a general strike across the public sector, including ATC. The difference is important as ATC strikes have generally more impact (more ppl on strike in the ATC sector).

Regarding cancellations, AF is not optimistic/pessimistic in its announcements: it is just following the Authority’s instructions to ensure a so-called minimum service (which is a more complex concept that it sounds: the goal is that every flight that is not cancelled ahead should be able to fly on the day of the strike, which obviously can lead to superfluous preventive cancellations… and eventually no delay if there is not as much ppl on strike as expected).