This is the octopus hose or rear heater hose. Where this plastic coupler meets the metal pipe, it’s not uncommon for these to leak directly on top of the hot catalytic converter and of course evaporate which won’t make it to the ground. I recommend using the mirror to see on the underside of this coupler to see if there’s any residue there. You may also see some residue on top of the cat. Take a few pix if you aren’t sure.