That’s untrue. The different readings result in different wordings and theology. One can also know that the Quran is not from God by finding scientific mistakes, which wouldn’t be present, if it came from an all-knowing being.The Quran is preserved. The different styles you're referring to have existed since the beginning and all of them are correct.
Ibn ‘Abbaas narrated that the Prophet (peace and blessings of Allaah be upon him) said: “Jibreel taught me one style and I reviewed it until he taught me more, and I kept asking him for more and he gave me more until finally there were seven styles.” (Sahih al-Bukhari)