Then it is supernatural. So what? It is like wuxia, martial practitioners can learn to do stuff that people in real life cannot. A lot wuxia is actually set on Earth, yet people accept this conceit just fine. It should be even easier to accept happening in a distinct fantasy setting where people can just learn to teleport and cast fireballs too.
And if you think wuxia is culturally too distant reference for campaigns set in medievalish pseudo-Europe, then think about Beowolf. The guy swam for a week straight in armour, ripped off an arm of a giant monster with his are hands and beat it death with it, could carry a monster's head that took four men to lift, and killed a dragon with a dagger. He could do this because he was badass fighter. Yes, it a story, but I think stories about mythic heroes fighting monsters and dragons is far more sensible reference point for D&D than the real life.