Cannot see why, upload the full video, maybe you hit standing water or the white lines were painted with the none grip paint which caused the LSD to shit itself and send way more power to the other wheel causing it to step out.
My view is in the wet if overtaking or on a faster type corner I hold light throttle so should it step out my throttle application is very small and as such the electronics if set to wet catch it easily and I've done nothing to really change the balance and weight transfer of the car.
In wet conditions, white lines, cambers in the road can easily cause a RWD to get a wriggle on especially a car with an LSD.
A perfect example, driving a GT3 in the wet, accidently putting one wheel on the curb, the LSD diverts power to the outer wheel resulting in a very quick and extremely hard to catch spin and yes I spun.
Then same corner, same curb but in a 911 Carrera S with open diff, same tyres, same weight balance, only difference lack of LSD, what happens, the inside wheel just spins up and the rear holds stable and I can just gently ease out to reduce the inside wheel spinning.
LSD's are great, especially for wet traction but only when the surface both wheels are on is the same, so white lines, patched areas of roads can cause an LSD to shift power and give you a bit of a shock.
Driving a high powered RWD car with LSD is like riding a bike, you need to look out for pot holes, patched sections of road, puddles, white lines etc. It is all part of the learning process.