the only thing baby metal has similar to Kpop is that it's an idol group, but their genre is not pop at all.

That's not quite true. In the beginning, the vocals were strictly Jpop while the instrumentals were metal with some more poppy passages.

Even now, though they've evolved a lot and one of them has even started to incorporate some false fold vocals, there's still some undeniable Jpop elements contrasting the metal.