The relevant quote there is:
The interior of the bus is configured with seating for 39 passengers including the
driver. Eight seats fold away for 2 wheelchair positions. The manufacturer passenger
placard indicates that the test bus can accommodate 42 standing passengers. At 150
lbs per person, this load results in a measured gross vehicle weight of 43,540 lbs which
exceeds the gross vehicle weight rating of 42,000 lbs by 1,540 lbs or approximately 10
people. At this load, the front gross axle weight rating is also exceeded. All testing
performed under this partial test was performed at a seated load weight of 37,230 lbs.
My read from that is total weight, and only about loading to highest placarded passenger count, which using the govt. weight would overload the axle.
I didn't see anything that would change based on weight location or CG.
As with every EV vehicle it's about weight reduction while maintaining structure and safety margins.