Asalaam O Alaikum
In discussions I've had with non Muslims, some have brought up these variant readings to try and say that there are different versions of the Quran,
If i was you and came across one of them, i would tell them that is why Prophet (saw) said
"Every Prophet was given a miracle and my miracle is the Quran."
Thats why Quran is a miracle because every word of the ancient Arabic which is in Quran gives out different shades of meaning and if all the Arabic words in Quran were limited to one single meaning, then it wouldn't be a miracle.
And that is why you can inform them we Muslims have Commentaries i.e. Tafsirs which are Scholars/Commentators who when translating the Quran comment on each and every Verse, because each and every Verse cannot just be limited to one translation. That is the beauty of Quran.
So one commentator of say for example 13th century CE wrote a commentary of the Quran and gave the literal translation as well as other meanings and signs that the Verse could be pointing towards in the age in which he was living, and wrote those points in the notes under that Verse which is commentary. All depends upon how much knowledge the one explaining the Quran has.
Then another Commentator came in our age for example and elaborated more on the meanings of the Verses or gave another very interesting interpretation of those Verses apart from its one basic translation, and helped the Ummah get better understanding of Quran. That is also why Scholars are heirs of the Prophets said the Prophet (Saw) himself.
A famous saying of Ali (r.a)....
Ali (ra) is reported to have said
‘If I wished I could load seventy camels only with the Tafsir of Surah Fatihah.'