The ancient Jews taught that it was wrong to even write the name of God. Since Christians took it upon themselves to write the name of God, what is the difference between writing an icon for the 99% of the population that was illiterate, and writing the name of God for the 1% of the population that could read? Besides, if we go back early enough, the Church taught subordinationalism and no defined Trinity; therefore these icons would have been considered orthodox at one time.
The icon was made in 500 AD or so then the icon would not have been orthodox. By that time the Church already held at least five out of seven Ecumenical Councils and the issue of Christology has long been settled.