This wording is what keeps the belt business going strong, if they only sold full grain leather the customer is very happy but won't be coming back unless they want to add another color or style.
Most belts that have the 'genuine leather' stamped deeply into the underside of the belt seem to be ok. If it is printed or on a label of any kind it means that the material won't take the stamping imprint well so it probably isn't worth your time either.
If it's reversible then it is not full grain anything. Real leather has a good face side and the rough underside with no need to fancy up the back with a glued up layer.
I bought a reversible Dockers belt once, in one day worth of wear the glued on leather layer was already wrinkled and blistering. I guess they are ok for playing dress-up once or twice.