'Does anti-establishment mean authoritarian? '
Absolutely not which is why Farage and UKIP want direct democracy, local democracy and local referendums on issues with more than 2 or 5 % popular support. Trump says the "system is rigged", rigged by the Establishment and its stooges who deny a democratic voice to the people as they do with the super delegate system in the US that allows the elites to override the will of the people and allows the party bigwigs to choose candidates that the donors and lobbyists approve of. It is teh same here with the Labour NEC removing the right to vote for the leader from many members. Trump, Farage and Corbyn want to end the rigged system, end the rule of the elites and the Oxbridge teams of cronies and as Corbyn says "break their magic circle". Anti-establishment is about taking power off the Establishment and its stooges and returning it to the people, it is populist, it is referendums where a "Mr Establishment" Owen Smith can't ignore the will of the people because he feels he knows what is best for us.
Anti-establishment was Brexit where we defied the stooges and "took back control" as Gove said, and denied the Establishment the ability to get their way. We beat them in a referendum, that is why they don't liek referendums. they say we are too stupid and like Owen Smith that they know best. But we don't believe them or the BBC and their stooges. the Corbynistas are reading the Canary above the New Statesman probably because they can all spot Establishment spin.
Anti-establishment is pro the people, pro democracy, and end to their rigged system that Trump will deliver.