"Well, actually" is a phrase used on the internet used to mock mansplainers, and pedants of various stripes and allegiances.
The usage of "Well, actually" might date from Gamergate, a confusing mess too confusing to explain, when certain of its proponents claimed that Gamergate was actually about ethics in games journalism. (Which was not what Gamergate was about). Since that point, it has taken off as a way to encapsulate the nitpicky and technical style of social media debaters.