Can’t find any evidence of that being a term prior to the tweet. I’d guess one of

• they meant something simple like ‘hateful dialogue’ or ‘hateful diatribe’, and thought it was a smart person way of saying it.
• it’s the dog whistle du jour. Somewhere on stormfront or voat they’re getting terribly worked up about ‘dialectical hatred’ as the new current threat to the white race.
• it’s used in some niche context where it has meaning. But our tweeter thinks it’s got more reach than it actually does.