Fantasy? I doubt it. I read it closer to the time I was an active duty specops officer, and I belived it all. I mean, it's historical record: he recruited officers and soldiers, trained them, got vehicles and moved his troops in columns and rescued the missionaries and aid workers all across Congo and killed countless terrorist "simbas".
The mainstream media never liked to bring it up though, because the CIA and mercenaries were VERY effective, while the UN and European govts were mainly impotent dolts.
Very comparable to the experience of the South African mercenary company "Executive Outcomes" in Sierra Leone in the mid 1990s: the globalists HATE it when private mercenary outfits are so effective. The UN and the RSA had EO thrown out of SL, and SL slipped back into horror. IOW, the UN prefers globalist (non) "control" and resultant horror to private military success, in the Congo in 65 or SL in 95.
That distaste is reflected in the elite media's treatment. The "fantasy" comment you spoke of very likely came from a leftist Che worshipper who could not believe that a bunch of mercs whipped Che's commie butt out of Africa.