He was made a Saint by the Churches East and West and was highly regarded in both his day and afterwards. He's not confused --- those who made him a Saint but then ignore his canonical list are the ones who are confused.
The reason they call him confused....is because Melito, like Polycarp and many other Church Fathers of the East, celebrated Passover (on the 14th) instead of Easter.
They, the Churches of the East, continued this observance well into the fourth century until they were prevented from doing so by the Council of Antioch (341 A.D.). The Council of Laodicea (364 A.D.) put the final nail of anti Jewishness into the Church by preventing Christians from celebrating the Sabbath on the seventh day.... as had Our Saviour and The Apostles.
I would venture to say that no copies of the Septuagint were to be found during these Passover celebrations jointly held with the Jewish folks.
Melito is recognized as a saint, but he lost a LOT of arguments, including the Quartodecennial controversy, which held that Easter should be held on the 14th of the month, no matter what. He also believed that God was corporeal.
He did create a canon without the Septuagint, but he also left out several New Testament books, as well; he, therefore, cannot be regarded as authoritative. He nearly could be charged with Judaizing.