The drums are the same except for the lug pattern and the hole size for the hub. I'm guessing that's what he means by that.
I guess your definition of 'same' is different from mine. Six lug and 8 lug drums are not the same and will not interchange.
I'm not aware of any trucks leaving the factory with 6 lug front and 8 lug rear axles. If there were, Id like to see documentation.