He's saying that His coming has fulfilled the prophecies of the Messiah, and that the other prophecies of the Old Testament are still in effect. People are free to interpret that passage as saying the entire OT is a complete literal accounting, but it's certainly a reach.

Please read a list of translations of that verse here, along with the original Greek https://biblehub.com/matthew/5-18.htm and come to your own conclusion of whether it has anything at all to do with a literal interpretation.