Actually, he wasn't. I am surprised by that poster, but have to assume it is real. Dylan was the headline act, Sunday night. Gordon was part of the "New Folks" concert on Sunday afternoon, which also included Hamilton Camp and Mimi & Dick Farina. I have the program of the "New Folks" session on the Hamilton Camp website here:
http://hamiltoncamp.com/Musician.asp
I am rather surprised that there was a poster giving Lightfoot almost equal billing with Dylan, because he was definitely a "new" artist then.