I think you are attaching too much importance to inferring the intent (flippant vs helpful) of Eliezer's one-line response to several dozen lines of discussion, and attaching too little importance to assessing the tone. In any case, the dictionary definition of flippant:

frivolously disrespectful, shallow, or lacking in seriousness; characterized by levity

seems to be about tone, rather than intent. Eliezer's comment qualifies as flippant. Nominull's response was also flippant by this definition. This matching tone strikes me as appropriate - which is exactly what I said.

At the point where Eliezer made his comment, he was being mildly criticized. His flippant comment, which I think was exactly truthful, carried the subtext that he was not particularly interested in discussing those criticisms at that time. He is totally within his rights sending that message. The criticism was mild, and formulating a serious and thoughtful response to the criticism is not something he was required to do. He could have just ignored it. He chose not to.

Sometimes clever, conversation-stopping responses don't stop conversations. Particularly when they are a little bit rude. Eliezer got a clever and rude response back. And for almost two years, everyone was satisfied with that ending.