Not sure where that priest got his information from, but how would everyone know the Justice of God if some information is withheld? Sorry, that priest is wrong.
SourceThe judgment will embrace all works, good or bad, forgiven as well as unforgiven sins, every idle word (Matthew 12:36), every secret thought (1 Corinthians 4:5). With the exception of Peter Lombard, theologians teach that even the secret sins of the just will be made manifest, in order that judgment may be made complete and that the justice and mercy of God may be glorified. This will not pain or embarrass the saints, but add to their glory, just as the repentance of St. Peter and St. Mary Magdalen is to these saints a source of joy and honour.