I don't think its that Left versus Right false paradim
Its more a deep, deep dislike for professional politicians in collusion with the ruling class consensus. Bernie Sanders was not Alt-Right, and Jeremy Corbyn is not Alt-Right.
For years, the really big issues that have divided society have been decided by magical consensus. Every serious political party decided to be pro-european, but the public has never ever felt that way.
What is more important to note is that they are preparing the narrative to blame Putin for the collapse of European Union.