No, a railroad is the situation where the PC takes what appears to be a reasonable action or reaction to the scenario and is foiled by GM fiat alone.
Well, fine. Let's use your definition.
Maybe you and I think of "fiat" differently. I don't think the GM imposing entirely plausible consequences for an action to be "fiat". The GM seems to have informed the player of the consequences beforehand, presumably because he felt they would be pretty obvious to the character. Sounds like an opportunity for the player to make an informed choice, to me. Is not informed choice the centerpiece of *non*-railroading play?
Kinda like, "Sure, you can attack that dragon, but you'll die, just so you know". Is killing a character who attacks a dragon they've been told is way too powerful to take on also "fiat"? I don't think so.