Bed dimensions are not fixed in stone. There are several king size bed references and the smallest is assumed to be 72" wide. A queen is nominally 60" wide. The narrowest of the vans is a Sprinter at 70" with Transits and Promasters wider. So calling a bed in a Class B a king is legitimate, IMO, that goes the width of a van as they are all wider than a queen.
2015 Advanced RV Ocean One Mercedes Benz Sprinter
Previous Class Bs:
2011 Great West Van Legend Sprinter
2005 Pleasure-way Plateau TS Sprinter