While some people view "railroading" as negative, i view it more neutral. Good or bad, it's primarily based on player buy, methods DM uses to keep things on the rails and do people have fun. Both Disneyland roller-coaster and Transsiberian railway are railroads, but one of them is fun twisty turny adrenaline filled ride, other is long, boring and mostly uneventful.
Situation from OP is textbook example of adventure staging in Ravenloft. You walk trough the mist and find yourself trapped in plane with very few ways of making back.
Most of my games in last decade or so could be called railroads. Part of it is cause i find sandbox games boring and part of it is cause i know my players and without guide rails, there would be lot of session time wasted on them deciding what to do. So i run games that are on the strong rails. Players have agency in how to deal with stuff, not so much in what stuff to deal with. It like theme adventure park ride. But, key here is, i have explicit player buy in. They are willingly staying on rails.