As I've said earlier, the issue is that people want to conflate railroading with linear. Generally, IME, because of this fetishization of sandbox play. "Well, I have no pre-determined plot, and all I have is this sandbox, so, I cannot possibly railroad", generally goes the argument.
That's why I usually go to my story about the gem merchant in Keep on the Borderlands. Keep is about as sandbox as it gets. You have virtually no prescripted plot in KotB. Yet, my DM very clearly railroaded.
And, the funny thing is, several people here tried to defend it. The players were being unreasonable by doing something the DM didn't want them to do. But, that's the entire point about railroading. DM's railroad when the players do something that the DM doesn't want them to do. That's the entire reason to railroad. Doesn't matter if you're in the most strictly linear or most wide open sandbox. The players are doing something that the DM doesn't like and the DM abuses his or her control over the game to enforce a specific outcome that is preferable to the DM.
This is why railroading as a gaming term is always negative. Let me repeat my point here. Railroading occurs when a DM abuses his or her authority at the table over the game world for the sole reason of achieving an outcome that is preferable to the DM. It's always a bad thing.
See, sure, you could handle this sort of thing at a Session 0 or outside the game. FANTASTIC idea. Totally avoids railroading and there's no abuse of authority going on. Granted, my example was from the early 1990's. The notion of "social contract" and "session zero" wasn't even a gleam in the eye of DMing advice. But, we have moved on considerably since then.
The problem comes when people try to apply the term railroading to situations that clearly aren't abuse of authority by the DM. That's where arguments over definitions come from. If I decide not to call for a skill check because the action is impossible, that's not an abuse of authority by the DM in 5e. That's what the DM is SUPPOSED to do. However, if I do call for a skill check, I should act in good faith if the check succeeds.
It's when the DM is no longer acting in good faith that we enter railroading territory.