I've seen yellow tail repeatedly head but and kill sharks - Ali has video of BFT hitting a Mako and likely killing it but I've never seen them using a shark's skin to remove parasites off their bodies. That would make sense based on the behavior.
That behavior is termed "chafing"-----it's presumed that the fish are rubbing ectoparasites off by swimming forward on the shark's abrasive skin, although in truth I can't remember seeing much in the way of ectoparasites on tuna. I've seen YT do it on a blue shark near San Pablo; there the YT would fairly vigorously rub along the side of the shark and then peel off just about at the pectoral fins.
Agree with the chafing as they take advantage of sharks skin and they follow behind at the sharks pace as they know of the danger. Have seen big yellows ram the stomachs of Blue Sharks off of Rocky Point back in the day to make them throw up stomach contents and if you had a dead squid ready its bendo. Swim pattern of Albacore seems be a stretch to do this ?
Maybe they’ve seen this guy end the fate of many tuna fighting for their lives on the line!? In open water it may be the tuna’s turn for some harassment lol. Really like the parasite theory though makes sense!