In terms of dividing fault, A350 pilot gets the most. Regardless of any clearance given the pilot is responsible for safe operations. And in a ground collision if one is stationary and one is in motion, fault goes mostly to the one in motion.
A good bit of fault, though less than to the A350 pilot, goes to the ground controller. Their whole job is to know where all aircraft are in real time, required separations, and to maintain safe flow of ground traffic. They should have seen the CRJ holding short of the correct position and told them to pull forward to the holding line.
CRJ pilot gets a small share of the fault for stopping short of where they should have.