robus
Lowcountry Low Roller
Railroads lead somewhere. Ergo, if there's no predefined endpoint, there is no railroad. GM fiat? Sure. Arbitrary constraints? Ok. But terms have meaning and if we ignore the meaning then the discussion is, unsurprisingly, meaningless.
I gave XP but then I retracted it when I thought about this some more.

Having an endpoint does not imply a railroad. Having only one route to the endpoint is a railroad. I.e the PCs can't have any impact on the way to the endpoint. They have to go through all the obstacles that the DM sets up - no deviation, no upsets, everything running as planned in advance.
Your definition would imply that every published adventure is a railroad and yet the stories told about what happens in individual games makes me think that players (and GMs) have a lot of leeway to go off the rails at any point and rejoin if/when it suits them.