So looking at the explorator class it was listed as having melee, basic, and pistol weapon proficiency (Universial). So did they change weapons proficiencies to make characters proficient in all weapons (so anyone who can shoot a stubpistol can also shoot a laspistol or a boltpistol?)
That would be my take on it with no additional information with which to postulate.
Basic Weapon Training - Universal - 500xp; gets you Bolt, Flame, Las, Launcher, Melta, Plasma, Primitive, and Solid Projectile trainning for Basic weapon types. But again, just my interpretation. We will know once the book is released.