He doesn’t say it is not a Jewish concept. On the contrary, he acknowledges that there are such Shitos while he apparently has a (very weak) Kasha on it.
This is besides the fact that Reb Chaim Kenievsky said that it was probably put in by someone other than the Rashash himself. I believe this as well. I think it is unlikely that he would argue on the Gra, or that would would ask this as a Kasha. Also, Baalei Gilgulim a funny term for the post-Zohar period.