From memory, buffet speed at MLW clean is about 200 KIAS (straight flight path). This will increase significantly if the aircraft is turning.
TAS around FL 220 ISA+10 with that indicated airspeed is about 290 KT
Looking at the FR ground speeds and even allowing for some error, these speeds tend to support the stall event scenario - what the events leading up to it were will be very interesting.
Be surprised if wake turbulence had much to do with it.