I have done many demo flights when working for aircraft manufacturers. There is a tendency for the VIP's on board (most of whom know SFA about aviation) to want to see the aircraft do manoeuvres that are outside of the normal civil operating envelope. Pressure can be put on the crew to demonstrate the agile manoeuvrability as the aircraft has low fuel and payload. Most of the time it is pulled off without consequences. This could well be one of those times it went wrong.
It's also perfectly possible, in my experience of demo tours, that the airline execs on board for the flight could have included one or more senior pilots from the potential customer.
Before assuming that both left- and right-hand seats were necessarily occupied by the Sukhoi crew at the time of the accident, it might be a good idea to wait for the CVR, if it's recoverable.