Most turbulence in thunderstorms is up and down drafts. Thus the general stresses on the airframe are negative and positive vertical G-loads that stress the wings the most, and the connection of the wings to the fuselage. Lateral stresses (yaw) that might snap a tail off are more common close to the ground in my (flying experience).
I would offer that *IF* the plane was structurally damaged and stopped flying ‘normally’ then then the aircraft might tumble or otherwise impact an airstream sufficient to ‘snap’ the tail off. OR the fuselage could have already been coming apart and those forces knocked the tail off. The fact that the rudder (the moving part) is still attached to the VS tells me that rudder input did NOT shear off the VS assembly.
My *opinion* is that the airplane quit flying and then the tail fell off.
NET: I doubt ‘turbulence’ on its own would knock of a VS.
N.B IIRC, a B-52 lost a vertical stabilizer in CAT (clear air turbulence) and SAFELY landed the aircraft after flying hundreds of miles to safety. I will Google that now for a reference
I’ve flown into some CAT’s in executive jets (I’m an FO on one) - lots of up and down but plenty of yaw too - almost circular in some instances - like a dog wagging its tail ...