Diognetus: Imputation

Was imputation taught in the early post-canonical church? Here's the very early (mid-second century?) and anonymous Epistle to Diognetus:

In whom was it possible for us, the lawless and ungodly, to be justified, except in the Son of God alone? O sweet exchange, O the incomprehensible work of God, O the unexpected blessings, that the sinfulness of many should be hidden in one righteous man, while the righteousness of one should justify many sinners!

HT: H. D. Williams, 'Justification by Faith: A Patristic Doctrine,' JEH 57 (2006): 654.