You seem to be defining railroading so broadly that any instance where the DM has any meaningful input in the game becomes railroading. That's not what railroading is. The Alexandrian defines railroading thus: railroads happen when the GM negates a player’s choice in order to enforce a preconceived outcome. I would define it as the DM removing meaningful and consequential choices from the player. Neither definition really applies to most of what you're calling railroading below.
I absolutely would not call that railroading. Limiting character creation choices in broad strokes isn't railroading. You're not completely removing meaningful, consequential choices from the player. Even drastically limiting choices, like say humans only, still isn't railroading. For character creation to be reduced to a railroad the DM would have to supply pre-generated characters.
They have a choice and are allowed to make it. You then prep the content they chose. Unless you prep the same content regardless of their choice, then it's not railroading. They have a meaningful, consequential choice. That's the opposite of railroading.
I disagree. The players being unaware of the railroad doesn't preclude it from being a railroad. The DM is removing meaningful, consequential choice from the players. That's railroading.