There have been plenty of fan-theories as to why Wolverine can suddenly generate heat from his adamantium-laced claws now that he's back from the dead. Some have posited that his new-found powers might be a callback to the less-than-stellar (look, it's really bad) Astonishing Spider-Men & Wolverine miniseries, during which Wolverine temporarily bonded with the Phoenix Force. And it's not a bad one, really -- it definitely plays into the themes of resurrection and the fact Logan has always had some sort of connection to cosmic entity, be it through Jean Grey or otherwise.
One of the most straightforward ideas is that we're seeing a simple second mutation. Now, why it took nearly two hundred years for it to pop is a big question, but if we apply the principle of Occam's razor, it's the most logical answer. Well, as logical as any theory about a semi-immortal Canadian with a skeleton covered in an unbreakable metal can be. If Wolverine's new "hot claws" are a second mutation, they wouldn't be the most bizarre or outlandish we've seen (remember when Husk went completely bonkers?).
But what if Wolverine's new power is based on something that happened nearly a century ago?
Comic books are great at playing the long game when it comes to storytelling. However, they are often played in reverse, by which we mean unresolved stories or left over tidbits of plot elements that were discarded at the time of publication can eventually be picked up years (sometimes decades) later to further develop characters or recon entire universes.
We see it happen all the time: A dead Robin can come crawling back from the grave twenty years later. Spider-Man suddenly turns out to be a clone couple hundred issues. Or there's celestial NDA mixed in with the primordial formation of the Earth which allowed for mutants and superheroes to exist and not get radiation poisoning from all the experiments they do (stop playing with gamma rays, guys). Maybe Wolverine's new power is somehow connected to the original Human Torch, Jim Hammond.
In 1939, the character of The Human Torch was introduced, but he wasn't the cocky kid brother of Sue Storm. Instead he was android created by Dr. Phineas T. Horton, a leading pioneer in developing artificial intelligence and robotics. His "son," Jim would wind up spontaneously igniting during a public unveiling of his creation due to the amount of volatile photoelectric solar cells (basically hyper aggressive solar panels) covering the android's body. In short, if Jim Horton was exposed to oxygenated air, he would burst into flame (pretty high concept, right?).
During the Golden Age of comics, The Human Torch would see plenty of deaths and resurrections. One such revival occurred when he is reignited by an atomic blast, which didn't last terribly long. It turned out the radiation would cause him to burn out. Years later, the android would be rebuilt by the Mad Thinker, only to combat his savior by sacrificing himself to save The Fantastic Four. There was even some back and forth business regarding The Vision actually being made of the remains of Jim for a spell. So how does this tie into Wolverine and his #hotclaws?