How do you know the priest was correct? And why would you let another person determine the state of your conscience?
The priest ONLY knows what I tell him, that is, his words are because of what I confessed. He can know nothing more of any penitent than what s/he tells him.
The priest is governed by the Ten Commandments...and God told us those. God determined our conscience many thousands of years ago.
His correctness follows those Ten Commandments, nothing more or nothing less.