TKS comes in 20 litre can/cartons - 6 of those would be 120 litres or about 130kg. With a 70-80kg pilot alone in the front and 130kg in the back seats then the CG would be borderline, that is assuming no other odds and ends in the baggage area.
If one applied a 'normal' control input on rotation in that configuration, not having given the aft CG much thought, then one can understand why the events that (allegedly) occurred, unfolded.