I think the BMS is housed inside of the HV battery pack, so to gain access they need to remove the pack from the car.
I can only speak from my experience on our one of our VW PHEV models, when we requested to attend a allocated dealership in Manchester to have a VW recall.
Which involved having the HV pack REMOVED from the car and the case split to check for water ingress, on our 2015 VW Golf.
The dealership was visited by a team of EV Tech' trained to remove the battery and strip the case to check for water ingress and treat accordingly.
NOT your standard dealership function with the greatest of respect.
That is why I am questioning what has been done by this dealership.
I would expect the guys at Long Bridge will have the tools and knowledge to pull out a pack.
Normal dealer level ??????????.