Wait, is this the slave we planned on rescuing? If so, could he not be Gondorian? You see, the only Gondorian slave played by somebody is Ferethor, but we don't want to rescue him (for story purposes, not that we want him to suffer!
). Instead, we should rescue one of the southron slaves, and decide which of the other characters he exactly is later.
But if the slave you rescued is not the slave we were planning on rescuing, then he can be a Gondorian.
Edit - And the party of soldiers (or at least most of them) are already belowdecks, freeing slaves. So, um, good job taking initiative, Kath.