No, that is not the same thing at all. Dual inventory fares are as described in HDDL's post #9: your fare is booked in a higher class (typically business) but the fare is a kind of notional add-on to an underlying lower class fare (typically eco). The idea is close to having an eco ticket which is instantaneously upgraded to a business ticket at booking time, with the consequence that you need availability in both the inventory for the corresponding underlying economy class and in the business class fare inventory in which you are booked.