I think that is
Psychological projection. In other words, what you are doing is 'projecting' your thoughts regarding how you would go about a conversation on the forum onto Truthseeker9. He does not 'like' to disagree, but since he disagreed with you he told you why he disagreed and presented his position. However, after a couple of posts he saw that it was just turning into an argument, so he opted out, since he does not like to argue. It is only from your perspective that "he refused to defend his claims." From his perspective he just does not like to keep responding when he sees that is never going to lead anywhere, since you are set in your opinions.
I know these things about him because Truthseeker9 (Duane) is my good friend and we correspond via e-mail all the time. For years, he told me I should not continue posting to a certain atheist on another forum who was never going to change his views. He was right about that, because that atheist never changed his views in over six years of posting to him almost daily.