Again you’re interpreting to mean “they can’t be cut” when in reality the can. What we see is that they can be cut, but they just get back up and the damage disappears.
The seraphim have that ability combined with the heightened durability as we’ve seen from Oda directly showing King and S-Hawk getting hit with a sword slash.
King and S-Hawk took the same move, zero damage on either of them. Zoro describes how King works and applies it to Lunarians, Vega doesn't interject.
This has been a weird headcanon in the community since the start, with zero evidence to support it in the manga.