It sounded different than Lehran.
Besides that, wasn't it Nasir who wanted to free the slaves in Begnion and bridge the beorc-laguz gap? There's also the thing with Dheginsea saying "Hold! Hold, I say!". That clearly shows that he's talking to a dragon, and he doesn't want him to leave the country (the policies they have and stuff). The whole conversation itself kinda hints that he's talking to a dragon (Nasir).
What would Lehran be wanting to do with Dheginsea, anyway? Wouldn't he have enough power to investigate and free the laguz slaves himself?