Again, people memorising a book is not evidence that the book is true, even if that book contains a promise that people will be able to memorise it.
People have memorised the Bible. You claim that not even the pope has. Even if this unsubstantiated claim is true, does that mean that no one else can memorise it? Many fundamentalist christians, I am sure, have memorised the Bible.
People have also memorised the digits of Pi. i think the record is about 30,000 digits of Pi. Does this tell us that the math gods are true?
And if the harry potter books have the line, "Your story is so remarkable, harry, that it wouldn't surprise me if one day everyone knew your story off by heart", would that mean that the Harry potter series is true if people memorise it?
And in any case, if you are too accept Islam as true because people have memorised the holy text of that faith, then should you accept that any religion is true if people have memorised that religion's holy text?