In this particular case, the item is guaranteed to he Heavy-Duty Boots. This is because the only ways to be immune to Sticky Web are Flying-Type, (hence the title) Air Balloon (Which reveals itself upon switch in anyway) and Levitate, but the only other way to be immune to Stealth Rock is Magic Guard. (and CAP's Mountaineer I guess) The two abilities can't be stacked, meaning not triggering both messages (Clear Body and co. trigger the Sticky Web message) guarantees the item is Heavy-Duty Boots, even in a hackmons scenario, since no other item allows the holder to be immune to either hazard.