“Kool aid” means something along the lines of “lies”. People usually say “drinking the kool aid” which means something along the lines of believing their lies.
The narrative associated with Jonestown of people being misguided in their thinking and so "drinking the Kool-Aid" may have been a major distortion. It's been some time since I read through the article in full. I'll try to see about re-reading it later, so I'm more clear on that point.