I don't see it as arm-chairing. Tim specifically asked for anything else he might have missed and was looking for other opinions. Evaluating yourself, and having others honestly do the same, for what you did and did not do is a great way of learning.
Arm-chairing, IMHO, is telling the guy he did it wrong and saying how the arm-chair QB would have done it better (which in Tim's case was not an issue).