I'm just going by how wikipedia and some other article, I think, report it. It looks like Haidt responded not to data, but to some complaints by libertarians who felt excluded.

Again, it says, "A sixth foundation, liberty (opposite of oppression) was theorized by Jonathan Haidt in The Righteous Mind, chapter eight, in response to economic conservatives complaining that the 5 foundation model didn't caption their notion of fairness correctly, which focused on proportionality, not equality."

https://en.wikipedia.org/wiki/Moral_foundations_theory#The_liberty_foundation