The “another poster” is me.
And the movie explains it perfectly. In fact, I believe the term, “gaslighting”, came about because of that movie, and never existed before that time.
(The movie is SO good!)
I am pretty sure you are correct there, that is the origination of the term.
To people such as conservatives who value truth, we have a particular distaste for gaslighting even apart from the sadism inherent in the usage of the tactic.
To leftists, it is just another implement in their toolbox, but one that they enjoy greatly due largely to its inherent sadism.
While we take great enjoyment in the deployment of truth to cause pain and discomfort in the Left, it is interesting to directly contrast that with the Left, which deploys lies in order to cause pain and discomfort in Conservatives.
Somehow, I think it relates to that saying:
“If you wish to make a Conservative angry, tell them a Lie. If you wish to make a Leftist angry, tell them the Truth.”
It's a great movie but not especially enjoyable for people who have experienced gaslighting in their previous marriage. ;-)