Sussed it
B5, E4,A3,D2,G1
Are meant for a 5-stringer.
Rather then make up 6-string bags, they just used the E6 from a guitar set.
Low B goes in the E6 bag and the others all shuffle along one so the numbers are right.
The could have put the high C in the E6 bag, but then the numbers would be wrong.