Maybe. Maybe not. Easiest way to find out is to ask them.
I think of railroading as meaning the GM is the one who decides all the outcomes. Whether the GM does that by deciding what s/he thinks is realistic, or in some other fashion, cuts across the issue. It doesn't determine it.
Why? (Assuming that it was meaningful in the first place.)
I mean, the assassination attempt could easily be railroading (depending on context). But if the players haven't taken any actions with the intention of affecting the ship (eg because they didn't know about it), then the GM deciding that the PCs (and thereby the players) now learn about the ship isn't forcing any outcome onto play.