Clearly he did it wrong, there's no strategy that will checkmate somebody on the first turn, so to speak. He should have anticipated the Basi and adapted accordingly, it's easy as it's only one model to work around rather than a whole army. Tip for fighting Stormcast. They're the Statline Army now like Chaos was in 8th, they have the most powerful models bar none by a long shot, I've seen five Stormcast Paladins take on ten Ogre Ironguts with the Ogres getting first attack and the Paladins massacred them. This is balanced out by the fact that the Stormcast have only the most basic synergies. In order to beat Stormcast, make sure you attack them with your entire army working as a whole and keep your synergy high, because if you don't do that and wind up in a straight up fight with few buffs, they'll walk all over you without breaking a sweat. And keep in mind that if your Stormcast opponent is a smart player, they will base strategy around preventing you from synergising and will try to force you to fight on their terms rather than on your own, so really try to control the battlefield as much as possible to prevent this from happening.
Just some food for thoughts... Is it possible to basically win in the first turn? I'd field something ala: Slann, Lord Kroak, EotS, Skink Starseer, Astrolith bearer, Oxyotl. with so few models, It's almost sure you'll be the one that chooses on Sudden Death scenario. You only have to choose Endure (Oxyotl). Your winning card disappears, and the rest of your models, proceed with a summoning of 8 units in the first turn. (of course, this tactic may be impossible, if you play with some of the current additional systems)
It's a good list unless you're playing Seraphon and the opponent goes first. Endless beaks before Oxyotl disappears. But the problem is finding a list that could at least come close to a first turn checkmate as it were. Obviously 2-4 large units of chameleons and a couple of units of 6-9 Rippers in a skink patrol could do a lot of damage combined with comets from Kroak. But a) I haven't got 18 ripperdactyls nor 80 chameleons! But I have been able to decimate my opponent first turn. (10% of his army first turn) But I do think that if models weren't a problem the list could be built that could get a first turn total victory.
We could even say that this kind of strategy, is one of the reasons that made clear the need for house rules. Heck, it's not even a strategy. .. it's a loophole.
Couldn't you also take a skink patrol and take a huge unit of rippers and a few chamos? You'd only place your skink priest on the board so would almost certainly get sudden death. Choose 'Blunt' and descend on that unit with fury and brimstone in your first turn. Game over.
Woah, very late on this, but... It could go very bad for you. It's the enemy that chooses what will be your target unit, so there are many things that can go wrong (I pick a unit that you cannot attack with rippers, or even better a unit that you simply cannot target at all, or a unit so well buffed that your rippers will die trying)