One day, I was strolling through Route 15, And found a heap of Shaking Grass, So i walked into it, Expecting an Audino, But to my surprise, I was a lv 50 Tyranitar!!! Is that normal???
Yes, if it was on Route 15. Audino isn't the only Pokemon to come out of shaking grass. Usually there is a chance, even if a small one, that a different Pokemon will come out. If this was not on Route 15, then your game is probably hacked or glitched. And please, next time look at the Pokemon's Pokedex page
to see if it is normal.