Granolah’s wish to be the strongest came true, albeit with a condition. The Eternal Dragon of Cereal, Toronbo was able to grant Granolah’s wish which made him the strongest mortal in the universe, apart from the Gods of Destruction and the angelic deity in Dragon Ball.
Dragon Ball Super manga chapter 70 revealed some new abilities and limitations of Granolah’s exponential powerup. As it turns out, the wish to become the strongest came at the cost of shortening his life span. The dragon granted his wish on the condition that Granolah will only live for three more years.
Not only did the wish increase Granolah’s power, but it might have also allowed him access to certain top tier abilities and moves as well.
At one point in the manga, Granolah destroyed a boulder with a huge explosion. Seeing this, several fans concluded that the powerup allowed Granolah to learn the Hakai technique as well. The only fallback to this conclusion being that Beerus had earlier stated that an explosion is the real highlight of the Hakai technique.
Interestingly, it seems that the movie isn’t an ordinary ki blast, since Granolah’s A.I. companion, Oatmeal was surprised at this new technique. And Oatmeal has been part of Granolah’s kit for a long time. Moreover, Macki from the Heeters group stated that the instantly vaporising move might be magic related.
However, since Granolah has never seen the Hakai or even knows about the technique, it seems a bit unlikely that the cerealian knowns Hakai. Moreover, since Beerus is teaching Vegeta the Hakai technique, Granolah simply being handed over this powerful move will downplay the fact that Vegeta is learning Hakai.
As of this writing, there is no evidence that Granolah has learnt Hakai, apart from just headcanon. The arc is still in its early stages so we’ll gradually be given more information as the story progresses. It’s better to wait for some more clarity before we jump to conclusions.