In context still means he forgives in the presence of Christ. Why? Because he is a disciple of Jesus. What he forgives is forgiven and what he retains is retained.
The man was already forgiven by the local ekklesia. Again, Paul is saying if they had forgiven him so did he....and why did he do this? So no advantage could be taken of by Satan.
Whether Paul agreed or not the local ekklesia had forgiven him.