By using this phrase, Paul was not trying to say that Jesus Christ is not himself human. Because Christ is both man and God, however, he is not a sinful human being. Paul is writing about where the gospel came from; that it did not come from other sinful human beings, but it came from Jesus Christ.
# it was by revelation of Jesus Christ to me
Possible meanings are 1) "Jesus Christ himself revealed the gospel to me" or 2) "God made me know the gospel when he showed me who Jesus Christ was."