The only reasonable conclusion here is that this is a "recovery/reduction of expenses and not truly rental income" or the sublease is actually rental income that is reported on Schedule E.
There is no such thing as a "sublease of a business" as that defies the very definition of the terms "sublease" or "subletting" (which relate specifically to renting of property by a third party). A sublease merely grants the exclusive right to possession and use, to a third party, of a portion of the original tenant's real estate (or of the entirety but for a shorter period of time than specified in the original lease).
Regardless, if a tenant leases real property from an owner thereof and grants a sublease to a third party, then by definition that tenant is renting out real property.
