When Bishop attacked Richthofen's squadron, he was unsure as to doing so because he knew they were the crack pilots, and so he just annoyed them by buzzing up and down. Innerved, the Germans went to get that Blue-nosed Neuport. I quite frankly belive that, based on the evidence, that he did come into contact with Richthofen more than once.
For more information on the subject, read
Billy Bishop's book "Winged Warfare" and also Arthur Bishop's book "Courage of the Early Morning."