Maybe there is a difference between conformity and collectivism; and between non-conformity and individualism. If a culture teaches people to worship individuality, and they do, that's conforming to the cultural rules. A non-conforming move in such culture could be e.g. to have a group of friends and decide things together; using the wisdom of crowds even if that is considered a heresy (but instead of "heresy" the culture would use its own low-status label, such as "stupid" or "immature").

The people in Jonestown probably considered themselves to be heroic rebels, against the mainstream society. But they were the "dressed-in-black" kind of rebels, instead of the "clown-suit" kind of rebels.

And the people who are "individualist" because the society told them that being "individualist" is a virtue and they never questioned it, and they are all "individualist" in the same way... that's like wearing a black uniform in a society where everyone is required to wear a black uniform. You can enjoy watching the horror on their faces when you suggest them to make something non-"individualist".

But I admit I wouldn't be able to predict whether being a "dressed-in-black" rebel is or isn't enough to dissent in the Asch's Conformity Experiment. I could explain it either way.