"545 AD and 568"
1) This was a typo. It was between 568 and 645 AD.
Here's the original article:
"Radiocarbon analysis has dated the parchment on which the text is written to the period between AD 568 and 645 with 95.4% accuracy. The test was carried out in a laboratory at the University of Oxford. The result places the leaves close to the time of the Prophet Muhammad, who is generally thought to have lived between AD 570 and 632."
2) They dated the paper, not the ink. It was common to scrape and reuse paper. It also only dates the time the plant or animal died.