It does look similar to Oshus's sword, but I'll have to take a minute on this. In Phantom Hourglass, Oshus's sword is flat out replaced with Oshus's sword. We have no idea where it is, probably floating around in the dream Great Sea.
So, perhaps Link had it remade, perhaps he kept it all this time, maybe this game actually takes place before PH and WW, and it turns out that some hero of the Ocean King's Great Sea used it to slay some foul beast, and Oshus kept it for safe keeping. However, that would have to take place after Bellum came into the playing field, for before then, the Ocean King was a whale. Wow, I'm getting off subject.
Anyway, we'll have to find out December 7th (Or 25th for those who are get it for Christmas) if it is Oshus's sword or just another recycled design.