When the Pharisees told the man to "Give glory to God," they weren't asking him to thank God for his healing. Commentators unanimously explain this was a formal command, like putting someone under oath, to confess a sin. Citing Old Testament examples like Joshua 7:19, they show the Pharisees were pressuring the man to admit the miracle was a fraud, essentially saying, "Tell the truth before God and confess your lie."