I wouldn't be surprised if there was another Murloc.
They added a ton of Murlocs to the Barrens, more than any other expansion, even though in World of Warcraft there is not a SINGLE Murloc in the Barrens or any neighboring zone, besides Dustwallow Marsh.
You can tell the new Hearthstone team have no idea about the lore and are just making it up as they go.
Well in one of the pictures you can see a neutral legendary murloc. When you look at the preview of the picture which was released, it looks like the legendaries are the bosses of the caverns. You can see a murloc (which was the endboss), a blue turtle, a nightelf and something else. In WoW there were nightelfs who shifted into snake form, so hopefully the legendary has some kind of effect like that, its also a druid card so most likely it will be a shapeshifter.
Hopefully Mutanas isn't strictly a Murloc-support card for Murloc decks, and is more of a general Murloc that has N'zoth synergy.
Except Mutanus is from the Nightmare, not related to the Old Gods. What kind of synergy would there be given N'Zoth, God of the Deep's battlecry?
He probably means it would be good if the murloc would be a good card by itself, without murloc synergies. Mostly, murlocs on their own arent really strong, but together they are. Well, the paladin prime murloc is good but neutral ones not so much