Railroading is, to me, when your players arrive at the same destination regardless of the choices they make (someone on these very boards said this once, and I made a note of it). Saying, "no, there's no shortcut" isn't railroading unless the intent is to make the players arrive at a certain destination. Railroading is based on intent, in my opinion. If I always say no because you always try to break genre expectations, cannot grasp the setting, are always looking for something that'd solve all of your issues, etc., I'm not railroading by fairly saying "no."
We're forking a bit down RR street, but your RR definitions makes me think of something.
I think of RR as a negative GM behavior, primarly actively thwarting valid player choices for the sole purpose of getting a specific outcome(s).
That might be defined as the "Micro" definition of railroading. In the active situation, negating player's valid attempts to do something, so they HAVE to do what you planned.
In the Macro-level view, this appears as "your players arrive at the same destination regardless of the choices they make"
I see "No" as being a powerful tool for the RRGM at the Micro level. "No, there's no airduct to escape from this room."
"No, that doesn't work."
"No, he has more friends that show up"
Even "Yes" can be twisted to a "No" as in "Yes, you start to climb the rough wall. However, one rock is loose and it falls out in your hand, and you fall down..."