I know I am in the minority here, but it is railroading IF you as a DM didn't set up a reason as to why and how all the exit points are blocked. And by that, I mean, if this was something that just kind of appeared out of nowhere, without interconnecting threads ting the big-bad in your climax to coercing or having control over the feywild's gates, then it would seem odd to me. Odd to me, and I wouldn't care. But to some, it could be considered railroading, if and only if, those threads weren't tied.