40 mph is quite fast so they could have been shut down for over speed, although that depends on the design. Its quite surprising how little wind it takes to over speed a wind turbine.
From the gridwatch yearly forecast France seems to only have about 10% wind capacity. If it was the peak time during the day the fossil fuel and nuclear plants would be at their normal rate and the turbines would likely be at the correct production rate. The turbines are quick acting so they may use the others you saw not working might be used to fill the gaps in demand while other traditional power stations are ramped up. In the UK we use diesel and natural gas gen sets for this, with farms of them strategically placed around the UK.
Energy supply is a tricky business now with the large amount of suppliers and reduction in coal power stations which we can ring online quickly.